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A COURSE IN
QUALITATIVE CHEMICAL ANALYSIS

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THK MACMILLAN COMPANY

UACMILLAN & C

THE UACMILLAN CO. OF CANADA, Lib.

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A COURSE IN

QUALITATIVE CHEMICAL

ANALYSIS

CHARLES BASKERVILLE, Ph.D., F.C.S.

LOUIS J. CURTMAN, Ph.D.

THE MACMILLAN COMPANY
1916

AH rigUs rtt4rvti

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^r .,-/

^•>.-:c-,,.''?;,

MAIN U»«»l<V-»"l='"-'''''« "=■■ •

COFmSHT, igio AMD 1916,

Bt the hacmillan company. i

Set up mil clectrotTPxl' Publiihcd December, igio. Sepilnted
Ociobcr, 1911; July, 191a; Jinuaiy, 1913; Febniuy, Octoba,

RcTucd cdilios, Scplcmber, October, igit.

thuUiig On. — Barwtsk A
Bgnrood, Mul. U.B.J

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PREFACE TO THE SECOND EDITION

The reception of this book by teachers of Qualitative Analy-
sis, calling for a number of reprintings of the first edition, has
been a source of gratification to the Authors. In the revision,
some changes and additions, as indicated by the use of the
book, have been made. The original plan of the book, how-
ever, has been maintained. Some valuable suggestions from
others have been utihzed- The theory of Electrolytic Disso-
ciation and the Law of Mass Action have been outlined. New
methods, some proposed elsewhere and some developed by
original work in our qualitative laboratories, have been incor-
porated. All of the new methods given have been thoroughly
tried out

THE AUTHORS.

N«w York Cmr,
JiHj, 1 91 6.

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PREFACE TO THE FIRST EDITION

Experience has shown the authors that a quantitative dis-
ciitninatioii in Qualitative Analysis for students is rarely exer-
cised, although it is generally conceded that qualitative analysis
should serve not only as a means for determining the compo-
nents in an " unknown," but also, though roughly, the propor-
tions in which the ingredients are present. This failure to gain
experience in the evaluation of tests is, we believe, largely due
to the fact that in the preliminary work which precedes the
analysis of "unknowns," adequate provision is not made
whereby the quantitative aspect as well as the qualitative
meaning of the results can he simultaneously studied.

In our work the quantitative feature is emphasized, first, by
early acquainting the student with the fact that there is a limit
in the quantity of an element in a definite volume that may be
detected by a given reaction ; second, by the use of known
solutions which are prepared to contain definite amounts of the
elements of a group in a definite volume. For example, the
label on the bottle states the metallic concentration of its
contents, and the student by using a specified volume knows
precisely how many milligrams of each metal he is using. The
advantages in the use of such a solution are : first, the size of
the precipitates may be controlled by the instructor and precipi-
tates of unwieldy hulk avoided ; second, and this is the chief
advantage, in addition to familiarizing himself with the reac-
tions and separations, the student also learns tke relation between
tke quantity of metal present and the size of tke precipitate which
it yields. The quantitative information thus acquired in the
analysis of known solutions is subsequently applied to the

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viii PREFACE

analysis of unknowns. In consequence of this training, the
student is able to report not only the qualitative composition
of his unkno\*ns, but also approximately their quantitative com-
position. The value of such training cannot be overestimated.
Our students rarely find any difficulty in differentiating between
a trace and a significant amount In the schemes of analysis
for the metals, preference has been given in a vast majority
of cases to precipitation tests, because of their quantitative
significance.

Detailed methods for the preparation of solutions of definite
strength are given for the assistance of the instructor.

The value of introducing preliminary experiments in a course
in Qualitative Analysis is a mooted question. We believe that
they should be restricted to those which are utilized in the
schemes of separation. Experience has shown us that it is a
good plan to have in the laboratory several sets of bottles con-
taining solutions of known strength of the salts of the various
metals. The students are encouraged to use these to verify
any of the preliminary tests in case of doubt By comparing
in special cases the results obtained with known solutions with
those obtained with the unknown, a definite knowledge of that
particular reaction is fixed in the student's mind. Students
should be encouraged to use short cuts, and the use of the
preliminary test as a means of indicating short cuts.

It is assumed that the student who begins the study of Quali-
tative Analysis has had a course in laboratory work in General
Chemistry, and has thus become familiar with such operations
as making solutions, precipitations, evaporations, ignitions,, and
the preparation of borax beads. He has also become familiar
with the term " solubility." For these reasons such matters
have received but scant attention in this book.

The student should have had not a little experience in writing
equations. The application of his knowledge, often meager,
to the processes of oxidation and reduction, as well as to the
mode of operation of reagents producing these changes, is not
always clear; or his knowledge is not sufficient to cope with
the cases met with in Qualitative Analysis. For this reason

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PREFACE ix

these matters have been brought together and coordinated with
some detail in the beginning of the book.

The essential features of this book may be seen from the
plan which is here briefly outlined.

1. The chief reactions of the metals are first given with suffi-
cient detail and completeness to enable the student to thor-
oughly understand the basis of and the limitations to the
schemes of analysis adopted. Reactions not utilized in the
schemes are also given to supply information which may be
turned to account in making additional confirmatory tests and
in devising schemes other than those given ; they also supply
a number of qualitative facts upon which important quantitative
methods are based. As the vast majority of students who take
Qualitative Analysis subsequently pursue a course in Quantita-
tive Analysis, this information supplies the foundation of fact
which we believe should be given in the qualitative course.

2. An outline of the method of analysis to be employed fol-
lows. This is in the nature of a r^sum^ of the chief reactions,
in which distinctions are emphasized with a view to their use in
separations. Details in manipulation are purposely omitted in
this discussion, in order that the main features and chemistry
thereof may be clearly understood.

3. The scheme of analysis is then taken up. The directions
are clear, especial attention being given to the amounts of
reagents to be taken, as well as the most appropriate vessel
to be used and its size.

4. Then follow notes. Under this head, additional informa-
tion, which would obstruct the reading of the text, is supplied.
This information is intended to supply the reasons for unusual
details or procedures in the text and precautions that are to be
taken, but it applies chiefly to matters relating to the correcting
of errors and to the clearing up of doubtful results. Supplying
the reasons for every step, it is believed, will go a long way
toward doing away with the too frequent practice of blindly
following directions.

The so-called rarer elements have been omitted, and some of
the commoner ones also, as their study is not essential in a

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X PS£BACE

first course in Qualitative Analysis. This is essentially a prac-
tical book and not the place to exploit any particular hypothesis
or theory. Its contents are directed toward the study of reac-
tions and the operations and methods made use of in the identi-
fication of unknown substances or mixtures. Discussions of the
theory of electrolytic dissociation and the mass action law are
now presented in courses in General Chemistry. These may
be further applied in lectures, which form an integral part of
the study of Qualitative Analysis, and are of especial value
when accompanied by collateral reading of special works on the
theoretical phases of the subject

The authors are aware that no direcdons, however detailed
and carefully written, can replace the resourcefulness of the
instructor ; he should be particularly observant during the first
laboratory periods when methods of work are about to be
acquired, and should be quick to give personal attention to
those who need it most There are those to whom skill in
manipulation comes naturally, but it should be remembered
that those not so gifted may, by perseverance and constant
practice, acquire an unusual degree of skilL A bright student
will soon learn that he may carry on two or more operations
at once, as filtration of one liquid while evaporating another,
without the suggestion of an automatic teacher; but the work
of the class as a whole will suffer unless the instructor is alive
and richly suggestive.

In the recitations, questions may be asked concerning
separations and tests, other than those given in the schemes,
but which are given in the descriptive portion of the book;
these serve to stimulate original thinking and give oppor-
tunity for the exercise of individual ingenuity. Written
quizzes have little value beyond securing figures for grading,
unless the papers, after being corrected, are discussed with
the students.

Well-known works on the subject have been drawn from
more or less. We wish especially to mention Fresenius, Pres-
cott and Johnson, Treadwell, Knoevenagel, and A. A. Noyes.
Conflicting statements appear in many books; in some cases

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PREFACE xi

consultation of the original sources sufficed, in others research
was necessary, to arrive at a decision.

We are indebted to Mr. W. A. Hamor, who assisted in fol-
lowing the proof sheets.

CHARLES BASKERVILLE.

LOUIS J. CURTMAN.

COLLKGB OP TRB CmT OP NKW VOUC,
NoTcmbef, 19101

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TABLE OF CONTENTS

Prefaces . . v, vii

iNTRODUCnOK

(a) Analytical Cheroistrf Defined i

(i) Terms i

(d) Theory of Electrolytic Dissociation ..... 4
(e) Law of Mass Action 12

(/) Equations . 20

(g) OsidatioD and Reduction ....... 23

(A) Classification 29

PART I

The Metai^. Descriptive and Analytical 33

PART II

(a) The Acms. Descriptive and Analytical 123

(j) Preluiinary Examination 160

PART III

Couplets Analysis

(a) SchemeforGroupIII inthePrcsenceofOiganicMatteriPhoB-
phates, etc 185

(6) Preparation of the Solation 189

(e) Alloys 192

(ff) Treatment of Insoluble Substances 193

(e) Add Analysis of Minerals and Metallurgical Producta . . 199

Appendix i. Table of Solubilities 201

2. Reagents 205

3. List 1^ Apparatus 2tt

4. Preparation of Unknowns 212

Index 217

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INTRODUCTION

That branch of chemistry concerned with the. problem of de- __,
termining the composition of substances or nimi,ii*S..i)f stibt |'
stances and identifying them is called Analytical CheiDlst^'. . .
Substances are identified by their properties *«hich,rfoE ^liy ^'ie^: '- -
substance, are unchangeable and fixed. The problem of identi-
fying a substance, therefore, resolves itself into a determination
of a sufficient number of the properties of the substance in ques-
tion. For a mixture of substances it is frequently necessary to
separate the components before the latter can be identified.

The term analysis is used in Analytical Chemistry to denote
the systematic examination of a substance, and includes all the
operations, whether analytic or synthetic, involved in the process
of identifying a substance. An analysis may be either qnallta-
tive or quantitatlTe. If we satisfy ourselves that a ten-cent
piece consists of copper and silver, our knowledge is qualitative;
but if we ascertain how much copper and silver are contained in
a given weight of this alloy, our knowledge becomes quantita-
tive. For qualitative purposes, only a few of the many proper-
ties possessed by a substance are utilized for its identification.
In general, those which are striking and most rapidly determined
are the ones selected ; chief among these are color, state of
aggregation, solubility, and certain chemical properties.

Terms employed in Qualitative Analysis
If to an aqueous solution of sodium chloride we add a water
solution of silver nitrate, a white, curdy, solid substance forms
and settles to the bottom of the containing vessel. The chem-
ical change, as evidenced by the formation of the new sub-
stance, AgCl, and brought about by mixing these solutions, is
called a reaction. The AgNOj solution employed to produce
this reaction is called the reagent. The solid, insoluble AgCl is

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2 QUAUTATIVE CHEMICAL ANALYSIS

called the predpitate. Any reaction which is accompanied by
the formation of a precipitate is called a precipitation reaction
and the process of forming a precipitate is known as preciplta-
tiott. If we allow the precipitate to settle and carefully pour off
the clear supernatant liquid, the process is known as decantatioa.
If, without allowing the precipitate to settle, we pour the liquid
■■:h9lding.the.gr.edpitate in suspension on a filter paper, supported
•ifr-a funnel- Sr^dtBer design of filtering apparatus, the liquid will
1 jpa^_:tjl^6jt^h th&fTne pores of the filter and will be thus sepa-
' "rSted 'fforh' W& ^rftcipitate, which will remain on the paper.
This process is known as filtration and is frequently resorted to
for the separation of a liquid from a solid. The precipitate on
the iilter is sometimes called the residue, while the liquid which
passes through is called the filtrate. The equation for the
reaction, omitting consideration of the water, is —
NaCl + AgNOg = AgCl + NaNOg.
Assuming that an excess of silver nitrate has been used, the pre-
cipitated and filtered AgCl will be wet with a solution containing
NaNOa and AgNOg. As these are soluble in water, it is evi-
dent that they may be removed by treating the precipitate on
the filter with water. The process of removing soluble impuri-
ties from insoluble substances by treatment with water is known
as washing.* All precipitates should be thoroughly washed.
Much time will be saved in washing precipitates by allowing
each portion of water completely to pass through the filter
before adding the next. The completeness of the washing is
ascertained by testing a portion of the last washings for the sub-
stance it is desired to remove. In the above case, after washing
several times with small amounts of water, the last portion
should be tested by adding to it a little NaCl solution. If no
precipitate is formed, the washing may be considered complete ;
if a precipitate or cloudiness is obt^ned, it is an indication that
all the AgNOg has not been washed out of the precipitate. In
the latter case, the washing should be continued until a negative
test with NaCl is obtained.

* Water is otcd here u the typical solvent.

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INTWDUCTIOir

General Directions for Laboratory Work

Order and cleanliness are essential to success in qualitative
analysis. It is a good plan never to put away apparatus until
the latter is clean and ready for use. Beakers, evaporating
dishes, and funnels, after being thoroughly washed, should
finally be rinsed with distilled water, inverted, and allowed to
drain and dry on a clean towel which has been spread out on
the floor of the cupboard of the desk. Every piece of appara-
tus in the desk should have a fixed place. Iron ware should
not be kept in the same drawer or compartment with glass ware.
Some attention should also be given to the arrangement of
apparatus on the desk. In general, the desk space should be
roughly divided into two parts — namely, one reserved for heat-
ing, and the other for filtering, washing, testing, etc. Reagent
bottles must never be allowed to accumulate on the desk, but
should be returned to their proper places immediately after use.
Accidents, which occasionally happen even to the most careful
workers, must receive immediate attention; the broken glass
should be collected and thrown into a special crock provided
for this purpose ; and the desk top should be sponged off, the
apparatus cleaned, and the analysis begun anew. Vessels con-
taining solutions or precipitates which are to be set aside for
future examination should be properly labeled.

Reagents. The bottles on the desk are iilled with solutions
known as reagents. They should occasionally be wiped off
with a moist rag and every effort should be made to keep their
contents pure. When once an impurity is allowed to enter a
reagent bottle, the reagent becomes worthless. The importance
of the care of reagents will be appreciated when it is remem-
bered that the value of the whole analysis is dependent upon
their purity. The bottles should always be kept properly
stoppered, and the stopper under no circumstances should be
placed on the desk, where it is likely to take up impurities and
thus eventually contaminate the reagent. The student should
make it a rule always to hold the stopper between the fingers
while using the bottle and to return it immediately after use;

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4 QUALITATIVE CHEMICAL ANALYSIS

in this way danger of contamination from the desk is avoided.
Acids of two strengths will be found on the desk. Before
using the reagents, the student should be sure that he is using
the proper ones. If he will learn in each case the reason for
adding the reagent, the error arising from the use of the wrong
reagent will seldom, if ever, occur. Too much reagent is worse
than adding too little. Reagents should always be added drop
by drop and should never be used in great excess, unless other-
wise directed; but under no circumstance is an excess of
reagent to be poured back into the bottle.

All operations which result in the production of fumes of
any kind must be conducted under the hood, with the window
of the latter almost completely closed.

The Theory of Electrolytic Dissociation*
When a substance such as sugar is added to water and the
latter stirred, there results a homogeneous mixture known as a
solution. The dissolved substance, the sugar, is called the
solute ; the water in which the sugar dissolves, the solvent. In
a similar manner we may prepare an aqueous solution of salt.
An experimental study of the properties of aqueous solutions
discloses the fact that some conduct the electric current, while
others do not; e.g., a solution of sugar does not permit the pas-
sage of the current, while on the other hand a solution of salt is
found to be a good conductor of electricity. It is natural to
suppose that the solute which is different in the two cases cited
is responsible for the difference in behavior. Experiment con-
firms this supposition. We may therefore divide substances
soluble in water into two classes, viz. (a) those which conduct
the electric current and {b) those which do not. The former
are called electrolytes, the latter non-electrolytes. Acids, bases,
and salts are electrolytes. Sugar, glycerol, urea, ethyl alcohol,
are non-electrolytes.

■ The theoietical matter dealt with in this lectioii is genendl^ con^deted more
oi leu in preUminary coana in Geaeial Chemiitrf. A brief summary ii here giveo
partly to refruh the itudent'i knovriedge, bat chieSy to emphasize certain pdnciplea
which have many appUcations in the &eld of qualitative analydi.

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INTSODVCTION 5

A study of the freezing and boiling pmnts of aqueous solu-
tions leads to a similar classification. Thus if 60 grams (the
molecular weight) of urea are dissolved in 1000 grams of water,
the resulting solution, which is said to contain one mole of urea,
is found to freeze at —1.86° C- The same result is obtained
when a solution containing one mole of any other non-electro-
lyte is cooled to its freezing point. In general, it has been
found that the freezing point of a dilute solution of a non-
electrolyte is solely dependent upon the number of moles in
solution, provided that in freezing only the pure solvent sepa-
rates out. Thus the freezing point of a solution of 50 grams of
methyl alcohol in 1000 grams of water is found to be —'2.90°.
This is what we should expect, since the number of moles in
solution is |^, or 1.56. And as the freezing point is lowered
1.86° for each mole of a non-electrolyte, the total lowering
should be 1.86 X 1.56 = 2.9a

On the other hand, if we dissolve -^oi a mole (5.85 grams)
of sodium chloride iii 1000 grams of water and determine its
freezing point, we should find it to be — 0.350°. If sodium
chloride were a non-electrolyte, the freezing point should be
— 0.186. On comparing these results we see that the lowering

is —^ , or 1 .88, times greater than that which we should obtain' if

salt were a non-electrolyte. A comparative study of the boiling
points of molar solutions of electrolytes and non-electrolytes
reveals a similar di£Eerence, viz. that solutions of electrolytes
boil at a higher temperature than solutions of non-electrolytes
of the same molar concentration. On the basis of an experi-
mental stud^of three of the properties of solutions, viz. con-
ductivity, biffiing point, and freezing point, we are thus led to a
division oif soluble substances into two classes, electrolytes and
non-electrolytes.

Moreover, a study of the reactions of electrolytes in solution
shows that they behave in solution as though their constituent
parts were independent of each other ; thus solutions of KCl,
NaCI, BaClj, and FeClg each give the same precipitate with a
solution of AgNOg, Ag,SO|, AgC,HgO^ or AgF. In other

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6 QUAUTATIVE CHEMICAL ANALYSIS

words, the chlorine in the first series of salts reacts independently
of the metal with which it is united to give a precipitate of AgCl
when any soluble salt of silver is added, the silver acting inde-
pendently of the acid radical with which it is united in the dry
state. In general, all electrolytes having a common com-
ponent will respond to a reaction that is characteristic of that
component.

All these differences in the properties of solutions of electro-
lytes and non-electrolytes find their explanation in the Theory
of Electrolytic Dissociation which was proposed by Svante
Arrhenius in 1887. According to this theory when an electrolyte
is dissolved in water, it breaks up or dissociates more or less
completely into electrically charged particles called ums. These
ions are of two kinds, viz, those carrying positive electricity called
cations and those bearing negative charges called anions. As
the resulting solution is electrically neutral, the sum of all the
positive charges in solution; must be equal to the total number
of negative charges. The change which takes place according
to this theory when an electrolyte is dissolved in water may be
formulated as follows : —

HCl5iH++CI-,

NaOH^Na++OH-.

NaCl^Na+H-Cl-

The above shows that dissociation is to be looked upon as a
reversible reaction. The extent of the dissociation varies with
the dilution ; and at infinite dilution, the dissociation may be re-
garded as complete. The -f- sign between the ions indicates
that they are to be regarded as independent particles with spe-
cific chemical and physical properties. The possession of a
charge of positive electricity renders the sodium ion (Na*') totally
different from the elementary substance sodium. The same
holds true for the hydrogen ion, which is distinctly different from
the electrically neutral hydrogen gas. Metallic sodium, as is
well known, reacts violently with water ; sodium ions do not
We usually recognize hydrogen ions by their sour taste and by
their property of changing the cotor of solutions of certain sub-

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IHTSODVCTION 7

staoces, called indicators. Hydrogen gas does not exhibit these
properties.

By passing a current through an aqueous solution of NaCl,
the electro-negative chlorine ions will travel toWards the positive
electrode, give up their charges to the latter, and become elec-
trically neutral chlorine, which exhibits the well-known properties
of this element The electro-positive sodium ions will at the
same time migrate to the positive electrode. Sodium ions
are not discharged at this pole owing to the fact that the
hydrogen ions, formed by the dissociation of the water, lose
their charges more readily than do the sodium ions. Conse-
quently on passage of the current, the hydrc^en ions lose their
charge and electrically neutral hydrogen escapes at the positive
electrode.

Before taking up the applications of the ionic theory let us see
how it accounts for the facts mentioned in the early part of this
discussion. Since the depression of the freezing point is de-
pendent upon the number of particles of the dissolved substance
in a given weight of the solvent, it follows that a solution of an
electrolyte should depress the freezing point more than a solu-
tion of non-electrolyte of the same molar concentration, for the
reason that in the former we should have a greater number of
particles, each molecule of the electrolyte being capable of yield-
ing at least two ions. The same explanation applies to the
observed differences in the boiling points. The existence of
electrically charged ions in solutions accounts for the conduc-
tivity of solutions of electrolytes ; and the failure of solutions of
non-electrolytes to conduct the current is due to the absence of
ions. Finally, we have to consider how the ionic theory accounts
for the independent behavior of the components of electrolytes
in solution, which, as already mentioned, makes it possible for
salts having a common component to respond to a common reac-
tion. Since all chlorides yield chlorine ions, it is perfectly clear
why they should all give a precipitate with any soluble silver
salt, for the latter, according to the ionic theory, supplies silver
ions. This can be best seen by writing the equations for the
reaction in ionic form: —

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8 QUAUTATIVE CHEMICAL ANALYSIS

Ag+ + NOg- + Na+ + CI- = AgCl + Na+ + NO," (i)

1 Ag+ + F- + NH4+ + CI- = AgCl + NH^+ + F" (2)

If we cancel in each equation the ions which appear on oppo-
site sides, equations (i) and (2) become : —

Ag+ + Cl- = AgCL

The last equation states that when silver and chlorine ions
are brought together, silver chloride Is formed; and as the
latter is a difficultly soluble substance, a precipitate of AgCl is
generally obtained. Hence we say that Ag ions are a test for
CI ions, and vice versa. From solutions, AgCl is formed only
by the combinatioQ of Ag and CI ions ; therefore solutions of
KClOg or CHCls do not yield a precipitate with silver nitrate
for the reason that no chlorine ions are formed by either of »
these substances in solution. Chloroform in aqueous solution
does not conduct the electric current, giving no evidence of dis-
sociation, and hence yields no chlorine ions. Potassium chlorate
does ionize in solution, but the ions are K* and ClOj".

Acids and Bases. In terms of the ionic theory an add may
be defined as a substance which, when dissolved in water, dis-
sociates with the formation of hydrogen ions.

Thus HCl5tH+-fCI-.

Dibasic acids dissociate in two and tribasic adds in three
stages, as shown below : —

(HaSO^ 5tH++HS04-,

Jhso,- ^H+ + S04~.

HgPOt ^H+-HHaPOt-,
H3PO4- ^H++HP04— .
HP04~5tH+-f PO4 .

Thus a solution of sulphuric acid may contain, besides the
undissociated acid, the ions H and HSO4. All the character-
istic properties of acids in solution — viz. (i) sour taste, (2) the
ability to change the colors of indicators, (3) the ability to give

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INTRODUCTION g

off hydrogen gas when treated with certain metals, (4) the power
to neutralize bases — are due to the presence of hydrogen ions.
The hydrogen ions are thus the active constituents of acid solu-
tions. The differences in the strengths of acids are due to
variations in the extent to which they are dissociated. We thus
distinguish two classes of acids. Those which dissociate largely
and thus supply a high concentration of hydrogen ions, and
those which dissociate slightly and thus yield a low concentra-
tion of hydrogen ions ; the former are called strong, the latter
weak, acids.

The active component of solutions of bases is the hydroxyl
ion (0H~), and to it are attributable all the characteristic prop-
erties of bases, viz., (i) the ability to turn red litmus blue, (2) the
alkaline taste, (3) the power to neutralize acids. We may define
a base, therefore, as a substance which, when dissolved in water,
dissociates with the formation of OH ions. The following are
examples : —

NaOH ^Na+ -t- OH".

I Ca(OH), :^ CaOH+ -I- OH"

lcaOH+ :^Ca++ -J- OH".

Di-acid bases dissociate in two steps as shown above. As in
the case of acids, we distinguish two classes of bases, depending
upon the degree to which they are dissociated, A strong base
yields a large percentage of OH ions; a weak base dissociates
feebly, yielding a small concentration of OH ions.

Salts yield on dissociation negative ions of the acid and
positive ions of the base, as shown here : —

NaCl ^Na+ -t-Cl^.

(NH4)aS0i5*:NHt+-f NH^SO,"
NH^SOr :?iNH4+-l-S04— .

CoBdnctlvity and Dissociation. The conductivity of a solution
is conditioned by the presence of ions, for the latter are the
means by which the current is transported through the solution.
Therefore, the greater the extent to which an electrolyte is disso-
ciated in solution, the greater will be its conductivity ; and, con-

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lo QUAUTATIVE CHEMICAL ANALYSIS

versely, the greater the conductivity of a solution containing sn
equivalent weight of an electrolyte, the greater will be its dis-
sociation. In the electrical conductivity of a solution, therefore,
we have a ready means of determining the degree of dissocia-
tion. In practice the resistance of the solution is determined
and from the latter the conductivity is readily calculated, the
conductivity being the reciprocal of the resistance.

In conductivity determinations, the results are generally ex-
pressed on the basis of equivalent quantities.

T/ig specific resistance of a solution is the resistance in ohms
of a cube of one centimeter edge. The specific conductivity is
the reciprocal of the specific resistance, and is therefore ex-
pressed in reciprocal ohms. The molar conductivity is the con-
ductivity of a solution which contains the molecular weight of
the substance in grams, contained between electrodes one centi-
meter apart. If, instead of the molecular weight, we use the
equivalent weight • in grams of the substance, we get the
equivalent conductivity. If we denote the equivalent conduc-
tivity by X (lambda) and the specific conductivity by k (kappa),
then we have X = a: x », where v is the volume in cc, which
contains the gram equivalent of the substance. An example
will make this relation clear. Suppose we wish to find the con-
ductivity of a o. I normal solution of HCl. We first determine
the specific resistance, i.e., the resistance of a i cm. cube of the
solution when the latter is contained between two parallel elec-
trodes. This is found to be 28, 5 ohms. Its specific conductivity

is therefore --— , or 0.0351, reciprocal ohm. Since the solu-
28.5

tion is tenth normal, one equivalent wUl be contained in 10 liters,
or io,ooocc. Therefore X = equivalent conductivity = 10,000 X
0.0351 =■ 351 reciprocal ohms.

The equivalent conductivity is found to increase with the di-
lution up to a certain point and then remains constant, so far as
measurements show. At this point of maximum conductivity,

* In the cue of monobaiic ta^ and their salt*, tbe equivalent and molar con-
ductivities will be identicid. Witti dibasic acids and theic lalt*, the equivalent will
be one half of the moleculai weight expiened in gramt.

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INTWDVCTIOlf H

the electrolyte must be completely dissociated into its ions, and
hence no increase in conductivity results on further dilution.
The maximum conductivity is generally referred to as the con-
ductiviiy at infinite dilution and is usually calculated from the
curve representing the conductivities for known dilutions.
Since the conductivity is proportional to the number of ions in
solution, it follows that the ratio of the equivalent conductivity
at a given dilution, to that at infinite dilution, will gine us the
percentage of the electrolyte that is ionized or the degree of dis-
sociation at the given dilution; or « = — ^, where* denotes the

M-
degree of dissociation of the electrolyte at the dilution v, /«, the
equivalent conductivity at the dilution v, and /i. the equivalent
conductivity at infinite dilution. An example will illustrate the
application of the above principle.

The specific resistance of a HCl solution containing 1.825
grams of HCl per liter is found by experiment to be 55.55 ohms

at + 18°.

36.5'-

— , of a gram equivalent. Therefore v, the volume which will

contain one gram equivalent (36. 5 g.)of HCl, will be 20 liters, or

20,000 cc. Hence «, = 20,oc» x = 360 reciprocal ohms.

That is to say, the equivalent conductivity of such a solution is
360 reciprocal ohms. The equivalent conductivity of an HCl
solution at infinite dilution at 18°, obtained by extrapolation
from the curve of conductivities of known dilutions, is found to
be 384 reciprocal ohms. Therefore « = ||| = 93.75 %. That
is to say, a solution containing 1.825 g- HCl per liter or ^a ^
molar solution of HCl, 93.75% of the HCl is dissociated into H
and CI ions, while but 6.25 % is in the un-ionlzed condition.

In the following table are given the approximate values of
the dissociation of the more common electrolytes met with in
qualitative analysis : —

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QVAUTATIYE CHEMICAL ANALYSIS

o.. Mo»»«. SoLonoH

H+Cl-i H+Br-; H+I"

; H*NO,-

H+ HSO,-

H+HC,0.-

H+HSO,-

H+H,POr

H+C,H,0,-

1-4

H+ HCO,-

0.12

H+HS-

aos

H+CN-

OXll

BASBS

K+OH-; Na+OH-

Ba+(OH-),

NH,+ OH-

1.4

8AIT8

Type B+A^KNOs, KCl) 84

Type B3+ A— or B++ A," (KaSO^, CaCl,) 71

Type B8+ A or B+++ Af (Kg Fe (CN)^ FeCl,) 65

Type B-^+ A— (MgSOj) 40

Pure water aoooooooz

The Law of Mass Action
In the following reversible reaction,

A + B:;tC+D,
let us denote the concentrations • of each of the substances by
[A], [Bl, [C], and [D] respectively. Let v represent the ve-
locity with which A and B react to form C and D and 1/ the
rate at which A and B are formed by the reaction between C
and D. Experiment shows that, all other things being constant,
V wiH be proportional to [A] and also to [B] and therefore to
their product, or

i'=!*x[A]x[B],

'These aie cipresKd in molei pet litei; thai ft HQ sotuUoa cantaining
1.835 B- HQ pet liter coDUini ^^^ = — mole ; or i cc contain 0.00005 ■Q'^'^-

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IKTSODVCTIOy 13

where <& is a constant dependent upon the nature of the sub-
stances reacting as well as upon the temperature. Similarly,
the velocity of the reaction in the reverse direction, i.e., the
formation of A and B by the interaction of C and D may be
represented by

At equilibrium, the velocities in both directions will he equal ;
and we have therefore

v=v' or A X [A] X [B] = ^ X [C] x [D], or
[C]x[D] _j:_„
[A]x[B] k •

Expressed in words the above equation states that the product
of the concentrations of the final substances, divided by the
product of the concentrations of the initial substances, is
a constant for any definite temperature for a reversible
reaction.

Where three substances are involved on each side of the equa-
tion, the same principle applies. Thus the equation expressing
the equilibrium for the reaction

A + B + C ij D + E + F would be IJliilfliil^ = K.

LAJ X [Bj X [^CJ

If two combining weights of any substance take part in the
reaction, then each is to be separately considered; thus the re-
versible reaction

A-t-2B:;^C + D may be written A + B + BqtC+D;

and the equilibrium equation becomes

[C]x[D] _K
[A]x[B]> ■

In its most general form, the law of mass action as expressed
in the above equation maybe stated as follows: At any constant
temperature, equilibrium will be reached in a reversibleTea(Aion,
when the product of the concentrations of^e final substances

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14 QUAUTATIVE CBBUICAL ANALYSIS

divided by the product of the coacentiatioas of the initial sub-
stances — each concentration raised to a power equal to the num*
her of combining weights reacting — is a constant

The Mass Action Lav and Ionization. As the ionization
of an electrolyte is a reversible reaction, we should expect
that it would obey the law of mass action. Experiment
shows, however, that while the mass action law rigidly
apphes to weak electrolytes, such as ammonium hydroxide
and acetic acid, it does not apply, for reasons which still
remain to be explained, to the dissociation of strongly ionized
acids, bases, and salts.

An example will illustrate the application of the mass action
law to ionization. A normal solution of ammonium hydroxide
Is found by experiment to ionize to the extent of o^%. loniza*
tion takes place according to the scheme

NH.OH :^ NH/+ OH- (i)

At equilibrium at a given temperature, we have

[NH.OH] '^ ^'>

Sub^tuting the values in the above equation, we get

°°°4''°°°4 _<,oooo.6.
0.996

Influence of Dilution. Let us suppose that a nonnal solution
of NH4OH is diluted n times. Then the value of each of the

concentrations in equation (z) will be reduced to - of its original

magnitude, and we have

i[NH,+]xi[OH-]

. [NH/] X [0H-]
i[NH.OH] " «[NH.OH]

<K.

The fraction will no longer be equal to the equilibrium con-
stant K, because the value of the denominator has been increased

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INTSODVCTION ij

m times its original value. In order to restore the disturbed
equilibrium, reaction (i) must proceed from left to right until,
by an increase in the concentrations of 0H~ and NHj+ and a
consequent decrease in the undissociated NH^OH, the ratio
again becomes equal to K, It is evident that the net result of
the dilution is an increase in the dissociation.

The Common Ion Effect. The ionization of acetic acid is
governed by the following equilibrium equation : —

[m]x[c,H,o,-] _K

[HCaHjOj]

Since a molar solution of acetic acid is ionized to the extent
of 042 %, we have, substituting in the above equation,

0.9958

If to this solution we add i mole or 82 g. of NaCgHgOj per
liter, the salt being 53 per cent, dissociated, the concentration
of the CjHbOj ions would be increased to 0.0042 + 0.53 = 0.5342.
if we substitute this value in the above equation, we get

' ^ liM which is no longer equal to the equilibrium con-

0.9958

stant 0.000018, and as a consequence the equilibrium will be
disturbed. The equilibrium can be restored only by an adjust-
ment of the values of the terms of the fraction. The denomina-
tor in the original equation for normal acetic acid when present
alone (0.9958), is so near its maximal value that any increase
in its magnitude (its highest possible value is i) due to a com.
bination of some of the H* and CjHgOj" — to form undissociated
HCjHjOa — will be negligible. We therefore need only consider
the concentrations of the ions in restoring equilibrium. The

new value for the concentration of the C»H.Oa~ ions is - °'^34
^ * ' 0.0042

or 126 times as great as it was originally, and therefore to re-
store equilibrium, the other factor, the concentration of the
liydrogen ions, must be reduced to y^ of its initial value ; i.e..

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i6 QVAUTATIVE CHEMICAL ANALYSIS

it will be reduced to -j^^ x 0.0042 = 0.000034. The net effect
of adding to a weakly dissociated acid a salt with an ion in
common is to reduce the concentration of the hydrogen ions or
to repress the ionization of the acid. A similar effect is pro-
duced when a salt with a common ion such as NH^Cl is added
to a weak base, such as ammonium hydroxide. The original
concentration of the OH ions will be reduced by virtue of an
increase in the concentration of the NH^ ions.

Solubility Product. In a saturated solutioa of AgCI equilib-
rium will be represented by the following equation : —

it^0El-k or [Agt] X [C1-] = * X [AgCl].

But since in a saturated solution [AgCl] is a constant, we may-
write the above equation in the form [Ag+] x [C1-] = K.

This equation states that for a saturated solution of a diffi-
cultly soluble electrolyte, the product of the concentrations of its
ions is a constant for a given temperature. This product is
called the solubility product*

With sparingly soluble electrolytes such as AgCl and BaSO^,
the dissociation of the dissolved substance may be regarded as
complete so that the concentration of the ions will be equal to
the solubility. An example will make this clear. The solubil-
ity of AgCl has been found to be 0.0000106 moles per liter.
The solubility product will be therefore (0.0000106).^

The application of the principle of the solubility product
to precipitation may be stated as follows : Whenever the
product of the concentrations of the ions, which by their
union are capable of forming an insoluble substance, is
greater than the solubility product of that substance, pre-
cipitation takes place. Conversely, when this product of the
ionic concentrations is less than the solubility product of the
insoluble substance, the latter, if present, will dissolve until
this value is reached.

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\ ■^•'

INTBODVCTION 17

lUustraHons. An aqueous solution of H,S behaves as a
weakly dissociated add. The equilibrium equation is

[H^-]'x[S--] _,^.
[H,S]

The addition of HCl to the solution will have the effect of in-
creasing [H+] and will correspondingly diminish [S~ ~] (common
ion effect). Now if a solution of a copper salt to which some
HCl be added f is treated with HjS, a precipitate is thrown
down. The formation of a precipitate is due to the fact that
the solubility product of CuS is exceedingly small and that in
spite of the repression of the ionization of the H^S by the free
HCl, the greatly diminished concentration of the S ions is still
sufficient to yield with the Cu ions a value greater than the
solubility product of CuS. On the other hand, if a zinc solu-
tion containing the same concentration of HCl be treated with
HjS, no precipitate of ZnS is obtained. The reason for this is
that although the solubility product of ZnS is quite small, being
much larger than that of CuS, the diminished concentration of
the S ions occasioned by the presence of the HCl is far too low
in value to cause the solubility product of ZnS to be exceeded,
however great the concentration of the Zn ions may he. If,
however, the solution be rendered alkaline, a precipitate of ZnS
is at once obtained. The addition of the base not only neutral-

* Hjrdiogea inlphide being a dibasic acid in tolatioii ionizes u follows : —

H^:?;h+ + HS-; (I)

HS-5?H* + S— . (a)

Tbe eqmUbriam cqaationi for (i) and (3) ire

[H+] X [HS-] [Ht]x[S— ] _.

[H,^ ^ [HS-] -**

Hultipljiiig these two equations together and cancelling, we get

[H«].x[S-] ^

[H^] 1 - -^

which is the equation ^ren above.

12.5 cc. cone. HCl in a volume of loO cc. of solution is a tnitable concentration.

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l8 QUAUTATIVE CHEMICAL ANALYSIS

izes the HCl present, thus causing an increase in the concentra-
tion of the S ions, but the HjS itself is converted into an alkali
sulphide whose degree of dissociation is vastly greater than that
of H^S, This enormous increase in the concentration of the S
ions accounts satisfactorily for the fact that in an alkaline solu-
tion the precipitation of zinc as sulphide by HjS is quantitative.

By an application of the principles involved in the solubility
product and the " common ion e£Eect," the student will readily
comprehend why an excess of the reagent is required to effect
a maximum precipitation of an ion. For example, in the pre-
cipitation of silver ions, it is customary to add an excess of chlo-
rine ions. The latter will reduce the concentration of the silver
ions to a negligible quantity and thus afford a practically com-
plete precipitation.

The solubility of CaCjO^ in an excess of HCl may be explained
from the standpoint of the ionic theory and solubility product
principle as follows : Experiment shows that oxalic acid is a
weakly dissociated acid ; hydrochloric acid, on the other band,
is a strongly ionized acid. In consequence of this difference,
the tendency, where the ions of both acids are in solution, will
be for the weakly dissociated acid to form. In the case under
consideration, some of the hydrogen ions from the HCl will
unite with some of the CjO^ ions derived from the CaCjOj in
solution, to form the weakly dissociated oxalic acid. The re-
moval of CgO^ ions from the solution will cause the product of
the concentrations of the Ca and €,04 ions in solution to fall
below the solubility product of CaC204. In consequence more
CaCj04 will go into solution in order to restore equilibrium ; and
this process of the removal of C^0^ by the H ions, and the solu-
tion of the CaCjOj, will go on until all the CaCjO^ is dissolved.
The reaction may be represented as follows : —

Ca++ + CjO,-- + 2 H- = HaCaOj -H Ca++

Hydrolysis. While the concentrations of OH and H ions in
water is exceedingly small, there being only ■nnju'innnr ^^ *
mole for each of these ions in a liter of water, they must be
taken into account in dealing with the behavior of solutions of

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INTRODUCTION 19

salts formed by the imion of a weak base with a strong acid,
and vice versa. Thus the student has already become familiar
with the fact that aqueous solutions of Na,COg and KCN possess
an alkaline reaction, while solutions of FeClg and CUSO4 are
acid to htmus. In the 'former case the reaction is due to the
presence of OH ions, while in the latter case the acidity is occa-
sioned by the presence of H ions in solution.

When potassium cyanide is dissolved in water, it dissociates
to a considerable extent into K and CN ions. We have, there-
fore, in solution for the moment K+ CN~ H"*", and OH". Now
on encountering the CN ions, the H ions will combine with
them, forming the very feebly dissociated acid HCN. The
removal of H ions from the solution will cause more water to
dissociate into H and OH ions ; the former will again be taken
up by more CN ions, and this process will continue until the
equilibrium constant for HCN is reached, i.e., until

[H^xECN-]
[HCN]

The removal of the H ions from the solution will result in the
accumulation of OH ions, and these will give to the solution its
alkaline reaction. The reaction may therefore be represented
as follows : —

K+ + CN- + H+ + OH- = HCN + K++ OH"

It is evident that the OH ions will not combine with the K
ions for the reason that KOH, even if formed, would be largely
dissociated in aqueous solution.

By a similar process of reasoning it may be shown why an
aqueous solution' of FeCIg possesses an acid reaction. In this
case, the weakly dissociated base Fe(OH)s is formed, which
removes the OH ions from the solution, thus causing an accu-
mulation of H ions from the progressive dissociation of water.
The final solution, therefore, will possess an acid reaction. We
may define hydrolysis as the process by which a salt of a weak
acid or base is decomposed into its corresponding acid and base
by the action of water.

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20 QUAUTATIVE CHEMICAL ANALYSIS

Equations
A chemical equation is a shorthand means of expressing a
reaction. The equation

BaCIj + HgSO^ = BaSO^ + 2 HCl

gives us, first, the quahtative fact that when BaCl^ solution is
treated with HjSOi, a precipitate of BaS04 is formed, together
with hydrochloric acid; and, second, the quantitative relations
between the substances reacting — namely, that 137 parts by
weight of barium in solution will require 9S parts by weight of
H^SO^ for its complete precipitation; or that (137 + 70) parts
by weight of BaClj, when treated with 98 parts of HjSO^, yield
(137 + 96) parts by weight of BaS04 and (2x36.5) parts by
weight of HCl.

In the case of gases, equations give us, besides qualitative

and quantitative relations, those of volume also. The equation

COa + C = 2 CO

states that when one volume of CO3 is reduced by the agency
of carbon, two volumes of carbon monoxide are produced.

Before writing an equation, we must first know the facts.
True, we may reason by analogy and foretell a reaction, and at
once write its equation ; but such equations are to be looked
upon with doubt until verified by actual experimentation.
Briefly, then, to write an equation, we must know the formulas
of the substances entering into the reaction, sometimes called
the factors and appearing on the left side of the equality sign,
and also we must know one or more of the essential products.
All of the latter need not be known; they can, with a little
knowledge, be " worked out." It is a good plan to designate
by means of an arrow pointing downward the formulas of
insoluble substances and with an arrow pointing upward the
formulas of gases ; e^g., a glance at the equation

\ CaCOg + 2 HCaHgOa = CUfZ^^O^ + HaO + \ COj
shows that CaCOg is a solid, that COg is a gas, and that the
other substances are in solution. Any determined method.

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INTBODVCTION 21

however, will answer the purpose, and as a rule it is applied
only to the products of a reaction.

The Law of the Conservation of Weight states that during a
chemical change there is no loss or gain In weight. From this it
follows that the total weight of the factors must be equal to the
total weight of the products. The Law of the Conservation of Ele-
ments states the immutabiUty of the elements during chemical
change. From the combination of these two fundamental laws
of chemistry, it follows that in any cheviical equation, the satne
number of combining weights of each element must appear on
both sides. This last rule, with a knowledge of the formulas of
the factors and products, suffices for the writing of an equation.
One need not attempt to remember the coefhcients appearing
in chemical equations, but should invariably work them out
The method of doing this will be explained later in connection
with the writing of a number of rather complex equations given
under " Oxidation and Reduction."

Types of Reactions

Reactions may be classed under three heads, viz. synthesis,
analysis, and metathesis. A synthetic reaction is one in which
a compound is formed from its elements, or, in general, a more
complex compound formed by the union of simpler ones, thus : —

Hj + Clj = 2HCl;
CaO+H,0 = Ca(OH),;
Fe(CN), + 4 KCN = K^FeCCN),,.

An analytical reaction is one in which some complex com-
pound is broken down into its elements or into simpler com-
pounds: for example: —
*^ "^ NaCl = Na + Cl;

CaCOg == CaO + CO,.

A metathetical reaction is one in which there is an exchange
of radicals ; these represent by far the largest number met with
in qualitative analysis ; for example : —

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22 QVAUTATtVE CBEMICAL ANALYSIS

(a) AgNO, + HQ = I AgQ + HNOj ;
(i) Cu(NOg),+ H^ = |CuS + 2HNO,;
{c) BaCl, + HaSOi = | BaSO, + 2 HCl.

Neutralization of bases by acids comes under this head.
NaOH + HCl =■ NaCl + HjO ;
NHjOH + HCjHgOa = NH^CaHgOa + HjO ;
Ca(OH)j + HjSOi = I CaSO^ + 2 HaO.

In some cases it is necessary to know the conditions under
which the reaction takes place before the equation can be
written; for example, if copper nitrate is mixed with dilute
HaSOj, no apparent reaction takes place, but if the mixture is
boiled till SOg fumes are given ofi, the following reaction
occurs : — CuCNOg), + HaSO, = CuSO^ + f 2 HNO,.
Similarly, on boiling, the following reactions will take place ; —
NH^CI + NaOH - NaCi + f NHg + HjO,
NaCl + H,S04= NaHSOj +t HCl ;
for, at these temperatures, HCl, NHg, and HNO, are evolved as
gases.

In writing a complicated equation, it is convenient to consider
the reaction as taking place in several stages ; • thus, when
ammonium sulphide is added to ao aqueous solution of AlClg,
a precipitate consisting of the hydroxide and not the sulphide
is obtained, and at the same time the evolution of HjS takes
plac?. This reaction becomes easily comprehended if we con-
sider it as taking place in two stages, viz. : —

(i) 2AlCl8 + 3(NH4)jS=AlaSe + 6NH4Cl;

but as AlaSg does not exist in contact with water, it decomposes
according to the equation

(2) AlaS, + 6 HaO = 1 2 A1(0H)b + f 3 H^S.

* Since we do not know what Ckuses chemical activitj, the ea^ mccbinism of a
reaction to nDkoown and is peihapi unknowable; any device tending to elucidate
or simplify a complicated reaction, it is believed, ibould be utilized, although experi-
memtal proof for theic devices cannot alwap be lupphed.

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INTBODVCTION 23

ComlHning(i) and (2), and eliminating A1,S^ which appears
on opposite sides of the equations, we get as the final equation
2 AICl8+3(NH4),S+6 H,0-.^2 Al(OH)8+6 NH,Cl+f 3 H^S.
Still more complicated equations will be met with which can
be readily written, if first resolved into two or more single equa-
tions, and the latter are then combined into one equation with
the elimination of c

Oxidation and Reduction

Oxidation niay be defined as a chemical change in which oxy-
gen or some other electro-negative element or radical is added,
or hydrogen or some other electro-positive element or radical
is removed. Redaction is the reverse process. The substance
which effects the oxidation is called the oxidizing sgeaX; and
that causing the reduction is called the redaclng agent. A con-
sideration of the following examples will make the matter
clear: —

Oxidation :

(i) 2FeO-«-0 = Fea08;

(2) FeCl3 + Cl=FeCl8;

(3) 2 FeS04 + HaSOi -I- Br, -= Fe3(S04)s + 2 HBr ;

(4) SnCl, + 2 HgCla = SnO, + 1 2 HgCl.

Reduction :

(5) CuO-«-Hj=Cu-(-HjO;

(6) 2 FeCIg -f- SnCIa « 2 FeCl, -f SnCl^ ;

(7) Fe,(S0i)8 + H, • = 2 FeSOi + HaSO, ;
(S) 2 HgCl, + SnCla = 1 2 HgCl -I- SnCl,.

The first four equations represent oxidation reactions, for in
each case oxygen or some other electro-negative element or
radical has been added. The last four are types of reduction
processes, for in each case oxygen or some other electro-nega-

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24 QUAUTATIVE CHEMICAL ANALYSIS

tive element or group has been removed. If we leave out of
consideration those simple cases of oxidation and reduction in
which there ia a. direct addition of the oxidizing or reducing
agent with the production of a single product, as in (i) and (2),
and carefully examine the others, we find that in every case
oxidation is accompanied by reduction, the oxidation of one
substance always involving the reduction of another; thus, in
example (4), the oxidation of SnClj has been accomplished at
the expense of the HgCIj, which has been reduced at the same
time to HgCI. In (5) the reduction of CuO has been simultane-
ous with the oxidation of H to HjO, Similarly, in (6) the reduc-
tion of FeClg has been accompanied by the oxidation of SnCl^
to SnCl,.

Further examination of the above eight examples of oxidation
and reduction shows that oxidation is accompanied by an increase
in valence, while in reduction reactions, a lowering of valence
is observed; thus, in (4) the valence of Sn has been increased
from 2 tQ 4, while at the same time the valence of Hg has been
lowered from 2 to I. In genera/, we may say that any reaction
in which there is an increase in valence is one of oxidation,
while a reaction in which there is a lowering of valence is one
of reduction.

Oxidizing Agents

The principal oxidizing agents are: oxygen, the halogens,
HNOj, agua regia, KClOg, Yif.xp^, KMnO,, Na,Oa, HjOjp
and PhOa-

The chief reducing agents are : nascent H, SnClj, H^S, HaSO, ;
and, at elevated temperatures, C, KCN, and organic matter.

The halogens either add directly ( i ) ; or else may be regarded
as oxidizing the acid by removing the H, setting free the acid
radical, which then adds on (2) ; or with bases by removing the
metal and thus leaving the hydroxyl radical (OH) to add on (3).
Examples of such changes follow.

(i) FeClj + Cl=.FeCl,;

(2) 2 FeSO^ + HaSO, + Clj = ^^SO^ + 2 HCl ;

(3) Fe(OH),+ KOH + Cl = Fe(OH)g + KCl.

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lUTFDDVCTION 25

Nitric acid acts as an oxidizing agent by virtue of its ready
decomposition according to the equation

2 HNOJ = 2 NO + H,0 + 3 O.

From this it is evident that 2 fonnular weights of HNO3 yield
3 combining weights of O. The liberated O may be regarded
as acting indirectly in the same way as CI ; that is, by oxidizing
the H of the acid and liberating the acid radical, which then
adds on, thus : —

(i) 2HNOa=2NO + HiO + 30;

(2) 3 HaSO^ + 3 Or= 3 HjO + 3 SO,.

Since 2 formular weights of FeSO^ require one SO4 for com.
plete oxidation, and since 3 SO4 radicals are made available by
2 HNOg, it follows that 2 formular weights of HNOg will oxidize
SFeSO,, to wit: —

(3) 6 FeSOi + 3 SO4 = 3 Fe^CSOiV

Adding (i), (2), and (3), and eliminating the factors appear-
ing on both sides in the equations, as 3 O and 3 SO4, the final
equation becomes —

6 FeSOi + 2 HNOg + 3HJSO4 = 3 Fcj(S04)8 + f 2 NO + 4 H,0.

Aqua regia is not only a good solvent but is also an excellent
oxidizing agent. Its action is practically the same as that of CI.
It is prepared by mixing i part of HNOg with 3 parts of HCl.
When heated alone, it is said to yield NOCl and CI, according
to the equation 3 HCl + HNOg = NOCI + Clj + 2 HaO ; but in
the presence of an oxidizable substance all of the CI is available,
so that the equation with aqua regia may be written as follows : —

3CoS + 6HCl+2HN08 = 3CoCl,4-2NO + 4HaO+ + 3S.

If the action of aqua regia on a sulphide is long continued, the
liberated S will be partially or entirely oxidized to H2SO4 : -~

S-l-6C] + 3HaO = SOa + 6HCl;
SOj + H,0 = HaSO^.

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26 QUAUTATIVE CHEMICAL ANALYSIS

Potassium chlorate, KCIOg, when used in conjunction with
HCl, is a powerful oxidizing agent In effect it is similar to agtta
rtgia and chlorine, as the following equations will indicate: —
(i) 2KaOa + 2HCl = 2HC10B + 2KCl;

(2) 2 HClOg = H,0 + 2 ClOj + O ;

(3) 2HCl+.0 = HjO + Clj.
Adding (i), (2), and (3), we get the following : —

2 KClOs + 4 HCl = 3 KCl + 2 HjO + 2 ClOj + CI,.

Potassium dichromate, KgCr^Oy, contains the acid anhydride
CrOg; its composition may be represented by the formula

2 CrOg + KjO. As 2 CrO, will, on reduction, yield CrjOg + 3 O,
it is evident that one formular weight of KjCrjO^ possesses the
same oxidizing power as two formular weights of HNOg, both
yielding 3 combining weights of O. We therefore obtain the
following equation for the oxidation of ferrous sulphate by
KaCraO^ : —

6 FeSOi + KjCrgO, + jtHjSO, =

3 FejCSOA + KjSO^ + Cr^SO,)s + 4rH,0.
The reduction of 2 CrOg to CrjOg leaves the latter, as well as
K3O, behind. These basic oxides readily dissolve in HjSO^ with
the formation of sulphates which appear in the above equation.
The amount of HjSOj needed to balance the above reaction
may be calculated from the following considerations : Cr^Og
requires 3 formular weights of HaSO^ for its solution ; KjO
requires I, thus making a total of 4. In addition to this quan-
tity, we must consider the amount necessary to react with the

3 combining weights of O derived from the 2 CrOg ; this will
require 3 more HjSOj, making the total 7, which becomes the
coefficient of H^SO^ in the above equations. We should also
have 7 HjO in the right-hand member of the equation for a
reason which must be evident to the reader.

Potassium permanganate, KMnO^, behaves in acid solution as
K,0 + 2 MnO + 5 O = 2 KMnO.;
that is, 2 KMnO| yields 5 combining weights of O.

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INTRODUCTION 27

The equatioQ for the oxidatioa of ferrous sulphate by KM11O4
may be written from the following considerations: 5 combin-
ing weights of O will liberate 5 SO4 radicals ; but as one SO^
suffices for the oxidation of 2 FeSO^, it is evident that 2 KMnOf
will oxidize 10 FeSO^, and we get the equation —

2 KMnO^ + 10 FeSOj + S HjSO^ =

5 FejCSO^)^ + 2 MnO + K,0 .+ 5 HaO.
However, KjO and 2 MnO readily dissolve in HjSO^ with the
formation of sulphates ; three additional fonnular weights of
HgSOf must therefore be added to the above equation, together
with 3 formular weights of water produced by the solution of
the oxides in the acid. The final equation becomes —

2 KMnO^ + 10 FeSO, + 8 HjSO, =

5 Fej(S04)8 + 2 MnSO, + K3SO, + 8 H,0.

Sodium dioxide, Na^Og, acts as an oxidizing agent by virtue
of its instabiUty in water or when it is heated in the presence
of an oxidizable substance in consequence of which it gives off
oxygen : — ^^q^ + HaO = 2 NaOH + O.

A solution of hydrogen dioxide, HaOa, also serves as an oxidiz-
ing agent for the same reason ; —

HjOa = HjO + O.

Na,Oa is, however, preferable to HjO,, for the latter can
only be safely* used in diluted fotro (3 9&), while the fonner
can be used in any concentration. NajO^ has the further ad-
vantage of supplying at the same time sodium hydroxide. For
oxidatioc in alkaline media, therefore, Na^Oj is the better reagent.

Lead dioxide, PbOg, like NajOj, yields O according to the
equation — p,jQ^ ^ pi,Q ^ q

It is employed to effect oxidation in acid media, as in the
conversion of MnO to HMnO^; the PbO is converted by the
excess of acid present into a salt

* A 30% solotiaD hu recently become rerf ntefnl in the Uborator;, egpecially in
the bandi of eipericnced chemiiU. We regaid the above lUtement at paiticnlulr
applicable to Rndent woik.

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a8 QUAUTATIVB CHEMICAL ANALYSIS

Reducing Agents

Any oxidizable substance can be utilized as a reducing agent, .
since, in order to reduce, it must be capable of oxidation.

Nascent H • acts as a reducing agent by either adding itself
directly (i) or by its ability to unite with, and thus remove, the
halogens contained in the compound (2): —

(1) As + 3H=AsH8;

(2) HgCla + 2H = |Hg + 2Ha

Nascent H may be prepared by the action of an acid or alkali
on certain metals : —

Zn + HjSOj = ZnSO, + 2 H ;

Zn + 2 NaOH = Na^ZnOa + 2 H ;

Al + 3 NaOH = NajAlOa + 3 H.

Nascent H may therefore be employed in both add and alkaline
media.

Stannous chloride, SnCl,, acts as a reducing agent, preferably
in an acid solution, by virtue of the ease with which it readily
oxidizes to SnCl4 : —

SnCla + 2 HgCla = SnCl^ + |2 HgCl ;

SnClj + 2 FeClg = 2 FeCla + SnCl, ;

HgAs04 + 2 HCl + SnOa = HjAsOg + HaO + SnClj.

Hydrogen sulphide, HjS, by virtue of the readiness with which
it decomposes into H and S is a reducing agent The hydrogen
acts as nascent hydrogen, while the sulphur separates out in the
solid state. Nearly all oxidizing agents are reduced by H,S with
the separation of sulphur, thus : —

2 HNOa + 3 HaS = 4 HjO + 2 NO + 3 S.
Hence, sulphides soluble in HNOg, like those of Fb, Bi, and Cu,
do not liberate HgS, because the latter at once acts on the

* Naicent H is used heie to designate tbe hydrogen which is fonncd when the
acid and metal or alkali and metat are both in contact with the solution to be
reduced.

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INTSODUCTION 29

excess of HNO) present with the liberation of S, as indicated
in the equation above. Halogens, aqua regia, ferric salts,
potassium permanganate, and chromates are also reduced by
HgS with the separation of S, and, in some cases, with a change
in color of the solution (see pp. 60-61).

Sulphurous add, HjSOg, and the sulphites easily remove
oxygen from compounds with the formation of sulphuric acid
and sulphates respectively, thus : —

HgAsO, 4- HjSOg = HgAsOg + HjSOj.

While HgSOg is an excellent reducing agent for arsenic when
in the pentavalent condition, it cannot be used in a complete
analysis if the alkaline earths are known to be present, because
of the formation of HjSOf as one of the products of the reduc-
tion. The reduction of arsenic compounds with H^SOs is best
accomplished in a pressure bottle at icX)° C.

Carbon acts as a reducing agent by virtue of its ability to
oxidize to CO and COj, thus : —

CuO + C + (heat) == Cu + CO.

The use of potassium cyanide, KCN, as a reducing ^ent in
the *' dry way " depends upon its ability to take up O and
formKCNO: —

SnOa + 2 KCN - Sn + 2 KCNO.

CLASSDFrcATION

In the analysis of a solution for metals, it has been found
-convenient to first separate them into groups by the use of cer-
tain reagents known as group reagents.

If to a solution containing all the metals in the form of salts
we add a slight excess of dilute hydrochloric acid, a precipitate
consisting of the chlorides of silver, mercury (-ous), and lead
will form. These metals are classed together and designated as
the first gronp. If, now, the precipitate of the chlorides of the
first group is filtered off and the filtrate, which is acid from the
«zce3s of HCl used, is treated with a stream of H,S gas, there

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30 QVAUTATIVE CHSMICAL ANALYSIS

will form a precipitate consisting of the sulphides of mercury
(-ic), lead,* bismuth, copper, cadmium, arsenic, antimony, and
tin. These metals are therefore classed together and col-
lectively are known as the secood groap. If the filtrate from
the second group is rendered alkaline with ammonium hydrox-
ide,t and then ammonium sulphide is 'added, a precipitate
of the hydroxides of aluminum and chromium, together with
the sulphides of iron, nickel, cobalt, manganese, and zinc, will
form. These constitute the third group. The filtrate from this
group will contain an excess of NH^OH and some NH^Cl.t
in addition to all the metals not included in the previous three
gTQups. If to this filtrate we add ammonium carbonate in slight
excess, a precipitate consisting of the carbonates of barium,
strontium, and calcium will form ; these constitute the fourth
group. . The final filtrate will contain all the other metals not
precipitated by the previous group reagents; they are magne-
sium, sodium, potassium, and ammonium, and these form the
fifth group.}

The division of the metals into groups is thus seen to depend
upon their behavior, when in solution, towards certain reagents
added in a certain order. If we were to use different reagents,
the grouping would be different It is eqbally important to
remember that the order of the addition of the reagents is as
vital for the above classification as the choice of the reagents ;
for if we were to reverse the order, — 'i.e., begin with NH^OH,
then add (NH4)jC0g and then (NH4)jS, — we should get quite a
different classification. It is furthermore to be noted that each
reagent, taken in the order given, is capable of separating its
own group from those which /c//i?w and not from those which

* Since FbGi is somewhat soluble in water, some of it will pus into the filtrate
&om Group I. and will be precipilated in the second group ai sulphide. Pb, there-
foie, belongs to both groups.

I When the solution which is acid with HO is rendered alkaline with ammonium
hydioxide, NH|C1 fonns; the -presence of this salt prevents magnesiom from precipi-
tating along with the metals of Group III. For the same reason, raagnesiam i« not
thrown down in the fourth group.

X The rarer metals are not considered in the text. %iecial treatises more or less
elaborate are necessary when they are included.

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mTBODVCTION

precede it in the regular order. Below is given in tabular form
the separation of the metals into groups with the formulas of
the compounds which are formed.

Solution coataiuing all the metals in the fonn of salts. Add HO and filter.

Precipitate: AgCl,
Group I.

FUtiate: Groups ll.-V. + excess HO ; pass in H^
and filter.

H«S, f bS,
Bi^, CuS,
CdS.As^„
Sb^„ SuS.
Group II.

FUtrate: Gr«up8 III.-V. + HCI+H^;
make alkaline with NH.OH, add
(NHJjS and filler.

Precipitate :
Al(OH)a,

Cr(OH)„
FeS, NiS,
Cos, MnS,
ZnS.
Group III.

Filtrate: Groups IV.-
V. + NH4CI ; add
(NHJjCO, and filter.

Prec^ttate:
BaCO»
SrCO„
CaCO„

Group IV.

PUtiate:
contains
Mg, Na,
K, NH^.
Group V.

It is thus seen that —

Group I. includes those metals whose chlorides are insoluble
in water and in dUute acids, and are hence precipitated by HCL

Group n. includes those metals which are not precipitated by
HCl, but whose sulphides are precipitated by HjS in acid solu-
tions. The sulphides are, therefore, insoluble in water and in
dilute acids.

Group UL includes those metals which are not precipitated
either by HCl or HgS in acid solution, but are precipitated by
{NH4)jS in solutions alkaline with NH^OH and in the presence
of NHjCI.

Group IV. includes those metals unprecipitated by the reagents
of Groups I., II., III., but which are precipitated by (NHj)5,COg
in the presence of NH^CL

Group V. includes metals not precipitated by the reagents of
Groups I.-IV.

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PART I

THE METALS

Reactions of the Hetals of Gronp I

The metals, silver, mercury (-ous), and lead, comprising this
group, are distinguished from all others by the insolubility of
their chlorides in water and in dilute acids. With the exception
of the nitrates and acetates, which are colorless, nearly all the
salts of the metals of this group are insoluble in water.

Silver
I. Hydrochloric add or a solnble chloride, when added to solu-
tions of silver salts, gives a white, curdy precipitate of silver
chloride (AgCl) which darkens on exposure to light. The pre-
cipitate is insoluble in water, the solubility being approximately
I part in 700,000 parts of water ; it is insoluble Ik dilute acids
and in dilute aqua regia, but is somewhat solulMe in concen-
trated acids. Ammonium hydroxide readily dissolves it, with
the formation of silver ammonia chloride [Ag(NHg)^CI] : —

AgCl + 2 NHa - Ag(NHa)aCl,

from which AgCl reprecipitates on^idification with nitric acid : —

Ag(NHB)aCl + 2 HNOg = i\gCI + 2 NH^NOa-

Silver chloride also dissolves in solutions of potassium cya-
nide and sodium thiosulphate; when cautiously heated, it fusea
without decomposition.

3. Hydri^en Sulphide and salable salpbides precipitate black
AgjS, insoluble in cold dilute acids, alkali hydroxides, and alkali
sulphides ; it is soluble in hot dilute HNOg, with the formation
of AgNOg and separation of sulphur. The reaction can be con<

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34 QUAUTATIVE CHEMICAL ANALYSIS

sidered as taking place in two steps, the first consistiiig of the
solution of the sulphide with the Hberation of HjS and the
second of the oxidation of the HjS by the excess of HNO,
present with the formation of water, nitric oxide, and the sepa-
ration of sulphur : —

(i) Ag,S + 2 HN0g = 2 AgNOs+fHjS;
(2) 2HNOa + 3HaS=4HaO+t2NO + |3S.
Multiplying equation (i) by 3 and adding it to (2), with the
elimination of 3 HjS, which appears on opposite sides, we get
as a final result : —

3 AgjS + 8 HNOa = 6 AgNOg + 4 H,0 + f 2 NO + +3 S.

Other insoluble compounds of silver are: —

AgBr — yellowish white ; Agl — pale yellow ; AgCN —
white; AggO — brown.

Silver is readily precipitated from its solutions by the more
electro-positive metals, as Cu, Zn, Hg, and Fe, as well as by
various reducing agents.

Mercury (-ous)
I. Hydrochloric acid and soluble chlorides give with solutions
of mercurous salts a white precipitate of HgCl (calomel), in-
soluble in water, the solubility being about i part in 300,cxx);
it is insoluble in cold dilute acids, but dissolves in strong nitric
acid and in a^tta regia, the latter oxidizmg it to HgCIj. Am-
monium hydroxide converts calomel into a black mixture of
finely divided mercury and NHgHgCI, insoluble in excess of the
reagent (this is the most characteristic reaction for mercurous
salts) : — ., ,

2ligCl + 2 NH8 = |(NH2HgCl-l-Hg)+NH^Cl. -
The black mixture dissolves in aqi4a regia with the formation of
mercuric chloride : —

(1) NHaHgCl -«- 3 a = +N -(- 2 HCl-J- HgClj;

(2) Hg+2Cl=HgGV
Adding (i) and (2), we get

NHaHgCI+Hg+5Cl = 2HgCla++N-!-2HCL

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THE METALS 35

2. Hydrogen Sulphide gives with solutions of mercurous salts
a black precipitate consisting of a mixture of mercuric sulphide
and elementary mercury; it may be assumed that the mercurous
sulphide which forms first, decomposes on account of its insta-
bility, thus; —

2 HgCl + HjS = I HggS + 2 HO;
HgaS = + HgS + |Hg.

3. Reducing Agents, as FeSOj or SnClj, rapidly reduce mer-
curous salts to metallic mercury: —

SnCla + 2 HgCl =» SnCl^ + + 2 Hg.

Lead

1. Hydrochloric add and soluble chlorides give with solutions
of lead salts, which are not too dilute, a white precipitate of
PbCl,, soluble in roo parts of Cold and 25 parts of boiling water;
from the latter on cooling, PbCla separates out in the form of .
needles. PbCl^ is much more insoluble in dilute HCl than in
water. Ammonium hydroxide changes it to a basic chloride
[Pb(OH)Cl] which is extremely insoluble in water.

2. Dilate sulphuric add and soluble sulphates precipitate white
PbSOf which is practically insoluble in H,0 (i part in about
30,000), but much more insoluble in the presence of dilute
HgSOf or alcohol. It is soluble to some extent in HNOg, and
is completely soluble in fixed alkalies and in a hot strong solu-
tion of NHjCjHgOa; from these solutions PbSO^ is repredpi-
tated on adding HjSOj.

3. Potassium Chromate (KgCrO^) precipitates yellow lead
chromate, readily soluble in sodium hydroxide, but insoluble in
NH4OH and acetic acid: —

PKCaH80a)a + KjCrO^ = | PbCrO^ + 2 KCjHaO,.

4. Hydrogen Sulphide from slightly acid solutions of lead salts
precipitates black PbS. In the presence of much HCl, H^S
either faib to predpitate or else produces a red insoluble com-

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36 QUAUTATIVE CHEMICAL ANALYSIS

pound of the formula FbCl, ■ 2 PbS; the latter is converted into
black PbS by treatment with (NH4)jS or by diluting the solu-
tion and passing in more HgS. Lead sulphide is insoluble in
dilute acids, alkali hydroxides, and alkali sulphides. Hot dilute
HNOj dissolves it with the formation of the nitrate and separa-
tion of sulphur. Hot concentrated HNO3 oxidizes it to sul-
phate.

PKNOb), + HjS = + PbS + 2 HNOy

With dilute HNO, this reaction occurs: —

3 PbS + 8 HNO,= 3Pb(NO,)a + + 2NO-l-|3S + 4HaO.«

With concentrated HNOg, the reactions may be represented
by the following equations: —

(i) PbS-»-2HN0j = |PbS04-|-2N0-HHj;
(2) 2HN08+3Ha = 2NO-|-4HjO.

Multiplying (i) by 3 and adding it to (2) with the elimination of
3 Ha, we get —

3 PbS -1- 8 HNO3 = 1 3 PbSOj -f- f 8 NO -H 4 H,0.

In a neutral solution containing i part of Pb in 100,000 parts
of water, H^S will distinctly reveal its presence. HjS is, there-
fore, an exceedingly sensitive reagent for the detection of Pb.

5. Sodliun or Potasslom Hydroxide precipitates white Pb(OH),,
soluble in excess : —

PbCCaHgOa), + 2 NaOH = | Pb(OH)j + 2 NaCjHgOj;
I Pb(OH)j + 2 NaOH = Na,PbO, -|- 2 HjO.

6. Ammonium Hydroxide precipitates a basic salt, insoluble
in excess.

Other difficultly soluble compounds of Pb are: —
Pblj — yellow; PbBrj — white; PbSO^, — white; basic car-
bonate — white, 2 PbCO, ■ PbCOH)^ ; PbCgO^ — white.

* RcMJvsble into two (tcpi, •> in the cue of the tolntion of AgiSin H{fO(.

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THE METALS 37

GROUP I
OatUne of tlie Process of Analysis

An examination of the foregoing reactions shows that all the
metals of this group may be precipitated by HCI. By filtering
off this precipitate, we should have on the filter a mixture con-
sisting of the chlorides of Ag, Hg {-ous), and Pb. In order
to identify the components oif this mixture, it is first neces-
sary to effect their separation ; this can be accomplished by
taking advantage of the difference of their behavior towards hot
water and ammonium hydroxide. PbClj is completely soluble
in hot water, while the others are practically insoluble. It is
thus possible, by treating the mixed chlorides with a suflicjent
' amount of hot water, to dissolve, or extract, the PbClg. If the
quantity of Fb is large, the hot aqueous extract on cooling
will deposit the characteristic needles of FbClg, and thus the
• presence of Pb may be proved. If the amount is small, the
water extract will require further testing to prove that it con-
tains Pb. The tests with H3SO4 and K^CrO^ will prove conclu-
sively whether or not lead has been extracted and therefore its
presence in the original solution.

Having extracted all the Pb, the residue on the filter may
consist of the chlorides of Ag and Hg. These can be readily
separated by reason of the solubility of the former in ammo-
nium hydroxide ; so that on treating the residue on the filter with
this reagent we should obtain a filtrate and a residue. The
former (if Ag is present) will contain the Ag in the form of
Ag(NH))]Cl, which, on acidification with HNOg, will yield a
white precipitate of AgCl.

While ammonium hydroxide dissolves AgCl, it offers at the
same time an indication of the presence or absence of Hg ; for
the latter in the form of chloride is blackened by the reagent.
To confirm the presence of Hg, the black residue is taken into
solution with aqua regia, whereby it is converted into HgClg,
and the latter is then tested for with SnCl,. A white precipitate
of HgCl or a gray precipitate of mercury (see this reaction
under Hg) proves the presence of Hg in the original solution.

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QUAUTATIVE CHEMICAL ANALYSIS

To the clear original solution contained in a smaU beaker, add
dilute HCl drop by drop with constant stirring until no further
precipitation takes place (i)"; add 2 cc, more in excess and
filter. If no precipitate forms, the absence of Ag, Hg (-ous),
and large amounts of Fb (2) is indicated ; in that case treat the
solution with HjS in accordance with directions given on page 62.
■^ The filtrate should be caught in a beaker of at least 150 cc.
capacity, labeled Groups II.-V., and reserved. The precipitate
is first washed with 2 cc. of dilute HCl {3), and finally with a
stream of cold water from a wash bottle. Reject the washings.
The precipitate may contain PbCl^ AgCl, and HgCl.

Pour through the filter holding the precipitate several small
portions of hot water, using about 2 cc. at a time and allowing
each portion to drain before adding the next Divide the
aqueous extract into two equal portions, and test it for Pb by
adding to the first portion dilute HgSOf — a white precipitate is
PbSOj ; to the second portion add K^CrOj — a yellow precipi-
tate is PbCrOj and confirms the presence of Pb. If no precipi-
tates are obtained, Pb is absent from Group I.

Repeatedly wash the precipitate on the filter paper with hot
water until the washings no longer react with dilute H^SOf.
The residue on the filter may now consist of AgCl and HgCl. -
Pour a few drops of ammonium hydroxide on the filter and
catch the liquid passing through in a test tube. Repeat until
about 1 5-20 drops have been used. A blackening of the residue
on the filter indicates the presence of Hg. The ammoniacal
extract, if not clear (4), should be passed again through the
same filter and tested for Ag by acidifying with HNOg (5). A
white precipitate or cloudiness proves the presence of silver (6).

To confirm the presence of Hg, remove (7) as much as pos-
sible of the black precipitate remaining on the filter to a small
evaporating dish, add 1-2 cc. of aqua regia {Z'){\^ drops of con-
centrated HCl to 5 drops of concentrated HNOg), and heat
under the hood on wire gauze until dissolved; boil. to destroy
the excess of aqua regia (9), dilute with i cc. of water, filter(ioX
* Tbe nnatben in btaduti taa to notei.

'\1

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.^ TEE METALS 39

if Qecessqgjtand test the clear solution for Hg by adding a few
drops of nblg. A white precipitate, vhich may turn gray to
black, confirms the presence of Hg.

1. A white predpitate, when dilute HCl is used, may be dae to SbOCI
or BiOO ; the latter, however, dissolves in excess of HCI.

To insure complete precipitation, HQ must be added in slight excess ; this
point is best ascertained by filtering a small portion of the mixture, and adding
to the deal filtrate a drop oi two of HCl, when, if the predpitation was com-
plete, no further predpitate will be obtained ; if a predpitate does form, more
HCl must be added to the wiginal solution until the test shows c<anplete pre-
dpitation. A large excess of HCl is to be avoided on account of the appre-
dable solubility of the chlorides in an excess.

2. PbCl, is somewhat soluble in cold H,0, and irtiile the presence of
HO diminishes its solubility, a small amount always remains unprecipitated
by HCl and passes into the filtrate, from which it is predpitated by H^ in
Group 11. One must therefore always loc^ for Pb in the second group.

3. The predpitate is washed first with HCl, instead of H,0, to prevent the
formation of the oxychlorides of Bi and Sb. It is then washed with H^O to re-
move the HCI, which would interfere with the scdution of PbCl, in hot water.

4- If all the Pb has not been extracted, it will be changed by ammonia
to the insoluble basic compound Pb(OH)CI, which InJQuently passes through
the filter. As this predpitate is soluble in HNO„ it does not interfere mth
the test for Ag.

5. In addifying a solution, it is imperative thoTOi^hly to mix the solu-
tion after the addition of the add,and then to test it with litmus. A solution
in a test tube can be mixed by pladng the thumb over the mouth of the tube
and shaking. If the solution is contained in a beaker, Uiorough mixing is
effected by stirring with a glass rod.

6. A doudiness or turbidity Is as condusivc a reaction as the formation
of a laige precipitate, provided the precaution is taken to sec that both the
solution to be tested and the reagent are perfectly dear. It is important to
remember that when the amount of Hg is large and that of silver relatively
small, ammonium hydroxide may &il to extract any AgCl, owing to the &ct
that the latter is reduced by the mercury of the blade mixture (NH,HgQ + Hg)
to the metallic state : — , . '-i,

2 AgQ -t- Hg = 3 Ag -H HgCI,.
When, therefore, a large black residue is obt^ned with ammonium hydroxide,
and the test for Agps negative, it becomes necessary to recover any Ag^e
black mixture may contain after the treatment with aqua regia as described
in note 10.

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40 QUAUTATIVE CBEUICAL ANALYSIS

1. When the precipitate is large, a small amount may be removed with s
glass or horn spatula. If too small to be handled in this way, recourse may
be had to one of the following methods : (a) The funnel containing the filter
is held horizontally with its rim resting against the edge of an evaporating
dish or beaker, and the predpitate is washed out by directing a forceful
stream of water from a wash bottle against the filter, at the same time giving
the funnel a rotary motion, (i) By carefiilly perforating the apex of the
filter with a platinum wire and gradually enlarging the hole (in this way dog-
ging of the stem with filter paper is avoided) ; the predpitate can then be
readily washed out with a forcefiil stream of water from a wash bottle. In
this case, as in (a), the ivattr should be cartfutty decanted after the precipitate
has settled and then the predpitate should be treated with the solvent directed
to be used, (c) Where the amount is very small and firmly adheres to the
filter, it can be gotten into solution by the following procedure : Remove the
filter from the funnel, close it up, and dry it by pressing it between the folds
of several thicknesses of filter paper ; then unfold it, tear away portions to
which no predpitate adheres, and spread the rest of the paper with the pre-
dpitate uppermost on the bottom of an evaporating dish. Pour the solvent
on the filter paper, heat, and stir with a glass rod till solution takes place ;
dilute with a little water and filter off the paper.

8. Aqwi regia should always be prepared in small amounts immediatelf
before use, and the cold mixture brought in contact with the substance to be
dissolved and then heated. In contact with a substance it is capable of dis-
solving, it acts like CI, and as the latter is an ozidizing agent, the chlcnide
formed will be that of the highest valence of the metal capable of existing
under the conditions.

9. Prolonged boiling has the effect of destroying aqua regia in atxmd-
acce with the equation

3 HCI + HNO, = NOCl + 2 H,0 + 2. 0.
The excess must be destroyed because its presence would oxidize the SnCl,
to SnCl,. As the latter does not react with HgClj, the test would be worthless-
10. The solution is diluted because of the possible presence of AgCI,
which is appreciably soluble in strong HCI. The residue, after filtration, is
tested for Ag by first thoroughly washing it with H,0, dissolving it in ammo-
ninm hydroxide, and repredpitating by addification with HNO^.

Reactions of MetaU of Group IX. Division A

Mercury in Mercuric Salts
Most of the salts of mercury are colorless and poisonous.
The aqueous solutions of the normal salts have an acid reaction
due to hydrolysis ; they all volatilize on ignition.

J^sV.

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TBB METALS 41

1. Potassium or Sodium Hydroxide gives a precipitate which
at iirst is brownish but rapidly changes on further addition of
the reagent to yellow HgO, insoluble in excess : —

HgCla + 2 KOH = |HgO + 2 KCH- H,0.

2. Ammonium Hydroxide produces in solutions of the mercu-
ric chloride a white precipitate of mercuric amido-chloride ; from
solutions of the nitrate, a white precipitate of mercuric amido-
nitrate : —

HgCL, + 2 NH4OH = INHjHgCl + NH^Cl + 2 HjO.

3. Hydn^en Sulphide, on being passed slowly into a solution
of HgClj, forms at first a white precipitate which changes on
further treatment with H^S to a yellow, then brown, and finally
to a black precipitate of HgS. These light-colored precipitates
are mixtures of HgClj and HgS in varying proportions ; they
are soluble in HNOg, and are converted by further treatment
with HjS or with (NH4XS to black HgS : —

3 HgCIa + 2 H,S = |(HgCl, ■ 2 HgS)+4HCl;
(HgCl, . 2 HgS)+ HaS = 4.3 HgS + 2 HCl.

HgS is insoluble in dilute HCl; also in hot dilute HNOg (differ-
ence from the sulphides of Pb, Bi, Cu, and Cd). Prolonged
boiling with strong HNOj converts it into the white compound
2 HgS ■ Hg(NOB)j, which is quite insoluble in dilute HNOa-
HgS is soluble in a^ua regia with the formation of HgCI^ and
the separation of sulphur; it is practically insoluble in (NH4),S,
but completely soluble in Na^S in the presence of sodium
hydroxide.

4. Stannous Chloride, added in small quantity to a solution of
HgCIj, precipitates white HgCl, which is reduced by an excess
of the reagent to black metallic Hg : —

SnOa + 2 HgCIj = | 2 HgCl -t- SnCl*;
2 HgCl + SnCIj = 1 2 Hg + SnGI^.

5. Ketallic Cn, Zn, or Fe, when introduced into a solution of
a mercuric salt, acidified, precipitates metallic Hg.

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42 QUAUTATIVE CHEMICAL ANALYSIS

6. PotasBium Iodide yields a red precipitate of Hgl,, soluble
in excess of the reagent or the mercury salt

7. If a dry mixture or a mercuric salt and Na,COg is heated
in an ignition tube, a sublimate of metallic Hg will be formed
in the upper portion of the tube.

Bismuth
Nearly all the bismuth salts are white or colorless. The
aqueous solutions always have an acid reaction, and if the dilu-
tion is large, the salt is decomposed with the formation of an
insoluble basic salt ; e.£: —

BiClg + HjO :^ \ BiOCl + 2 HCl.
This reaction is very characteristic of bismuth salts and is inter-
fered with by the presence of much acid. Because of their
tendency to hydrolyze with water, aqueous solutions of bismuth
salts can only be prepared with the aid of an acid.

1. Hydxogen Snlpbide precipitates black BijSj : —

3 HjS + 2 Bids = \ BijSb + 6 HCl.
The precipitate is insoluble in cold dilute acids, but dissolves in
boiling dilute HNOg: —

(i) Bi,S8+6HN08 = 2 Bi(N08)a + 3 HaS ;
(2) 3H3S + 2HNOB = |2NO+4HaO + |3S.
Adding (i) and (2), and eliminating 3 HgS, we get

BiaSj + 8 HNOg = 2 Bi(NOg)8 + +2 NO + 4 Ha© + | 3 S.
Bismuth sulphide is insoluble in (NH4)2Sj,

2. Potasslimi, Sodium, or Ammonlam Hydroxide precipitates
white Bi(OH),, insoluble in excess. Its insolubility in excess of
NH4OH distinguishes it from Cu and Cd; the precipitate is
soluble in dilute acids, however.

3. Water, when added in large amount to Bi salts, precipi-
tates white basic salts; the chloride gives |BiOCl, the nitrate'
IBiONOg, and the sulphate KBiO)aS04. These are all soluble
in dilute inorganic adds and are changed by HjS to BijSg : —

2 BiOCl -H 3 HjS = ^BigSg -I- 2 HCl + 2 Hfi.

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TBE UETALS

4. Soditun Stannlte ta aUcallne solatlan (prepared by adding
NaOH to SnClj till the precipitate which first forms dissolves)
gives with bismuth solutioDS a black precipitate of metallic

( 1 ) SnClj + 2 NaOH = \ Sn(OH)j + 2 NaCl.

(2) Sn(OH)j + 2 NaOH = NajSnOa + 2 H,0 ;

Sodlom aturalte

(3) BiCls + 3 NaOH = \ Bi(OH)s + 3 NaCl,

(4) 2 Bi(0H)8 + 3 Na^SnOj = 1 2 Bi + 3 HjO + 3 NajSnOs-
5. Hetallic Zn or Fe, when added to a solution of a Bi salt,

precipitates metallic Bi : —

2 BiCla + 3 Zn = 3 ZnClj +■!■ 2 Bi.

Copper
Copper forms two classes of salts ; viz., the cuprous com-
pounds, in which Cu is monovalent; and tlie cupric compounds,
in which Cu is divalent. The former are very unstable, being
readily oxidized to the cupric compounds ; they are insoluble in
water, but are soluble in halogen acids with the formation of
colorless solutions. The cupric salts, when dissolved in water,
yield blue or green solutions which have an acid reaction.

Reactions of the Cupric Salts

1. Sodinm or Potasslam Hydroxide precipitates light blue
Cu(OH)a, soluble in a lar^e excess of the strong reagent with
the formation of a blue liquid. The precipitate is changed on
boiling to black CuO. In the presence of sufficient tartaric,
citric, or arsenic acid, NaOH fails to precipitate Cu salts^

2. Ammooium Hydroxide, largely diluted and added cautiously
to solutions of copper salts, precipitates a light blue basic salt,
readily soluble in excess, producing a deep blue solution, due to
the formation of a cqpric ammonia salt : —

CuSO^ + 2 NH.OH = I Cu(OH), + (NHi)i,SOi ;
Cu(OH)j + (NH4)sS04 + 2 NH, = Cu(NHg)4SO, + z H,0.

Deep bine ■nliuloB

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44 QUAUTATIVE CHEMICAL ANALYSIS

When CuClg is used, the blue compouad formed with an excess
of NHj is Cu(NHg)4C]5. The sensitiveness of the test is i part
in 25,000; it therefore is an exceedingly good test except for
traces of the metal

3. Hydiogen Stilphide produces in Cu solutions a black pre-
cipitate of CuS which is insoluble in dilute acids and alkalies,
insoluble in sodium sulphide, but somewhat soluble in ammonium
sulphide, especially if the latter is yellow and hot ; it is insoluble
in hot dilute HjSOi (distinction from Cd). When freshly pre-
cipitated, CuS is easily soluble in KCN solution; it is also
soluble in hot dilute HNOg with the separation of S : —

3 CuS + 8 HNO3 = 3 Cu(N08)j + 4 HaO +f 2 NO + 1 3 S •
When exposed to the air in moist condition, CuS oxidizes to
CuSO^.

4. Potassiom Cyanide produces a yellow precipitate of
Cu(CN)j, which immediately decomposes into white cuprous
cyanide (CuCN) and cyanogen ; on adding an excess of the
reagent, the precipitate dissolves, with the formation of a com-
plex cyanide pf K and Cu : —

CuCla + 2 KCN = I Cu(CN)s + 2 KCl ;

■ 2Cu(CN)a = '^2CuCN + (CN)j;

CuCN -H 3 KCN = KbCu(CN)^ (potassium cuprous cyanide).

From solutions of KgCu(CN)^, HjS does not precipitate

CuS (distinction from Cd). If to the deep blue solution of

Cu(NHg)4S04 potassium cyanide is added, the color will be

bleached, due to the formation of K8Cu(CN)4: —

(i) 2 Cu(NH8)4S04 -I- 4 KCN =|2 Cu(CN)a-|- 2 KaSOj+S NH,;

(2) 2 Cu(CN)a = 1 2 CuCN + (CN)j ;

(3) CuCN + 3 KCN = KjCu(CN)4 ;

(4) (CN)j -»- 2 NH^OH = NH^CN + NHiCNO + HjO.

5. Potassium Ferrocyanide precipitates reddish brown cupric
f errocyanide : —

2 CuSOj + K4Fe(CN)B = | CujFe{CN)s + 2 KaSO,.
• Reiolvabk into 2 steps (lee PbS).

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TBE METALS 45

It is insoluble in dilute acids, but soluble in NH^OH with the
formatioii of a blue solution. The reaction with KjFe(CN)g is
by far the most sensitive test for Cu; with very dilute solutions,
it gives a reddish brown coloration. The sensitiveness of the
tests is I part in 200,000.

6. Potassium Iodide yields with solutions of cupric salts a
yellowish white precipitate of cuprous iodide (Cujlj); at the
same time iodine is liberated and turns the solution brown : —

2 CuCla + 4 KI = I Cujlj + 4 KCl + I,.

7. a Amino Normal Caproic Add.* An aqueous solution of
this compound when added to a solution of copper not too
strongly acid yields a characteristic crystalline precipitate of
copper a normal amino caproate. This is one of the most sen-
sitive tests for copper and is capable of detecting 0.004 mg. of ,
copper with certainty.

8. Certain organic substances, like glucose, reduce copper
solutions with the precipitation of red Cu^O. The test is best
carried out by adding to the copper solution KNaC^H^Qj
(Rochelle salt) and NaOH, the latter bemg added until the
resulting solution assumes a deep blue color. On boiling and
adding a small quantity of glucose, a red precipitate of CujO is
obtained. The reaction consists essentially of

2 CuO + (reducing agent) = | Cu,0 + O.

9. Many metals reduce solutions of Cu salts to the metallic
state; e.g:, Zn, Cd, Al, Fe. If an iron naU is immersed in a
solution containing a Cu salt slightly acidified with HCl, a bright
deposit of metallic Cu is formed on the iron. As dilute a solution
as I part in 120,000 of water will give this test.

Cu salts, when ignited in the bunsen flame, impart to it a
green color which is intensified if the Cu solution contains HCl.

Cadmium
The cadmium salts are for the most part colorless. The
nitrate, chloride, sulphate, bromide, iodide, and acetate are
soluble in water.

•Lyie, Cwtnum and Manball, J. A. C. S., 37, (1915). i47i-

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46 QVAUTATIVE CHEMICAL ANALYSIS

I. Potasslom or Sodlnm Hydroxide precipitates white
Cd(OH)^ insoluble in excess.

3. Anunonitim Hydroxide precipitates white Cd(OH)|, solu-
ble in excess, forming complex ammonia salts: —

Cdaa + 2NH40H = |Cd(OH)j + 2NH4a;
Cd(OH)| + 2 NH^a + 2 NHb - Cd(NH,)4Cla + 2 HjO.

. This ammonia salt, like the corresponding Cu salt, may be
transposed to the double cyanide, KjCd(CN)4, by a KCN
solution.

3. Hydn^en Sulphide precipitates, from solutions not too
strongly acid, yellow CdS, insoluble in cold dilute acids, alkali
hydroxides, and (NHj)jS; and insoluble in KCN (distinction
from Cu). It is soluble in hot dilute HNOg with the separation
of S (reaction similar to Pb, which see)^ and soluble in hot
dilute HaSO^ (difference from Cu).

From hot slightly acidulated solutions, H^S precipitates red
CdS.

L Cyanide yields a white precipitate, Cd(CN)^
soluble in excess, with the formation of KjCd(CN)4, from which
HjS precipitates CdS (distinction from Cu): — ■

CdCla + 2 KCN = | Cd(CN)j + 2 KCl;
Cd(CN)a + 2 KCN = K,Cd(CN)4;
KaCd(CN)4 + H,S = + CdS + 2 KCN + 2 HCN.

Reactions of the Uetals of Group H. Division B

Arsenic
Arsenic forms two series of compounds. Those in which it
plays the r61e of a trivalent metal are known as the arsemous
compounds; and those in which the metal is pentavalent are
known as the arsenic compounds. The two oxides AsgOg and
AsgO, are respectively the anhydrides of arsenious (HgAsOg)
and arsenic (HgAsO^) acids.

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TBE METAIS 47

RtactioHS of the Arsenious Compounds
The arsenious compounds may be considered as derived from
AsjOj. The latter, on treatment with boiling water, yields
HgAsOg; the oxide also dissolves in alkalies with the formation
of soluble alkali arsenites. All other arsenites are insoluble in
water.

AsjO, + 6 NaOH = 2 NagAsOg + 3 H,0.

1. NaOH, NH^OH, NajCOa, HCl, and H,SO. do not pre-
cipitate As from its compounds.

a. Hydrogen Sulphide. From neutral solutions of arsenites
or from aqueous solutions of AsgOg, HjS does aot precipitate
the sulphide but colors the solution yellow, which is due to the
formation of colloidal AsgSg : if, however, the solution is acidified
with HCl, a yellow precipitate of As^Sg immediately forms : —
2 HgAsOg + 3 H,S =. AsjSg + 6 HaO.

The precipitate is insoluble in concentrated HCl (distinction
from Sb and Sn), hence the presence of a large quantity of free
add does not interfere with the precipitation with H^S. Con-
centrated HNOg, aqua regia, or a mixture of concentrated HCl
and KClOg readily oxidizes AsgSg to arsenic acid (HgAsOg —
soluble in water) with the separation of S. Ammonium sulphide
and alkali hydroxides both dissolve As^g (distinction from the
sulphides of Division A).

3 AsjS, + 10 HNOg -»- 4 HjO = 6 HgAsO, -I- j 10 NO -H |9 S.

The action of aqua rtgia on As^Sg may be represented by the
following equations : —

AsaSg -I- 10 CI = 2 AsCl, -I- 1 3 S,
2 AsClj -H 5 HjO = AsaOj + 10 HCl,
AsjOb -t- 3 HjO = 2 HgAsO,.

Adding these 3 equations, with the elimination of substances
appearing on both sides, we get as the final result : —

AsgSg + 10 Cl-H 8 H,0 =. z HgAsOg -J- lO HCl -I- 13 S.

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4$ QUAUTATIVE CHEMICAL ANALYSIS

The action of KCIO, + HCl may be represented thus : —
KClOg + HCl - HCIOb + KCl ;
HCl + HClOi = HjO + ClOj + CL
It is evident that this mixture behaves somewhat like aqua regia.
The deportment of KOH is as follows : —

AsjSa + 6 KOH = KjAsOg + KgAsS, + 3 H,0.
KgAsSg may be regarded as derived from potassium arsenite
(KjAsOs). by replacement of the oxygen by S; hence it is
called potassium thioarsenite. If this mixture of thioarsenite
and arsenite is acidified with HCl, As^Sg is reprecipitated : —
KgAsOa + KgAsSg + 6 HCl = 6 KCI + 3 HjO + 1 AsaSj.
The equation for the solution of As^Sg in {NHj)gS is —

AsjSg + 3 (NHJjS = 2 (NHjV^sS, (ammonium thioarsenite).
If (NHj)jS, is used, we get ammonium thioarsenate : —
As,S,+ 3(NH,),S. = 2(NH,),AsS, + (3x-5)S.
The excess of S in the polysulphide oxidizes the thioarsenite
to thioarsenate. The {zx— 5)8 does not separate out but dis-
solves in the excess of (NH^^S, to form a higher polysulphide.'
If the solution of As,Sg in (NH4)aSj is acidified with HCl,
the As is reprecipitated as yellow AsjSj : —

2 (NH4)8AsS4 + 6 HCl = + Aa,Sj + 6 NH,C1 + +3 HaS ;
but as this solution always contains an excess of (NH4)tS;c the-
following reaction will also take place simultaneously: —
(NH,),S, + 2 HCl = 2 NH^Cl + 1 HjS + \ix - i)S.

3. Sflver Nitrate precipitates from neutral solutions of arse-
nites yellow silver arsenite, Ag,AsOg (distinction from arse-
nates) : —

KgAsOg -I- 3 AgNOg = \ AggAsOg + 3 KNO,.
The precipitate is easily soluble in acids and alkalies.

4. Magnesium mixture (solution of MgClaH- NH^Cl'+NH,)
does not precipitate arsenites (difference from arsenates),

5. Iodine in solutions rendered alkaline with NaHCOg readily
oxidizes arsenites to arsenates : —

NagAsO,+ Ij + 2NaHCO,= Na^04+2NaI-l-H,0-l-t2COr

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THE METALS 49

Special TMtf for the Detection of BUnnte AnMWinti of Arsenic
I. Tlie so-called llanh Teat for arsenic and its modifications is liased on
the fact that when arsenic compounds are introduced into a hydrogen generator
(Zn + HjSOJ, the As compound is reduced to gaseous arsine (AsHJ, which
escapes along with the excess of hydrogen. If the dried gases are led into a
hard glass tube heated to redness, the arsine wiU be decomposed and a de-
posit of metallic ai^enic will form in the tube just beyond the part heated.
If the gases are ignited, they bum with a bluish white flame; if apiece of cold
porcelain is held in this flame, it will receive a black coating which is readily
soluble in a solution of sodium hypobromite (NaBrO) (distinction from Sb).
In making this test, it is necessary to run what b called a blank to make sure
that the apparatus and the reagents employed in the test are arsenic-free. This
is accomplished by carrying out the test precisely as described, except that no
arsenic compound is added ; and if the materials are arsenic-free, no mirror
will be formed. Unless the results of this test are controlled by a blank, it can-
not be considered trustworthy, for ordinary pure zinc and sulphuric acid, as
well as glass tubing, usually contain sufficient arsenic to yield a positive result.
For the detection of arsenic in wall paper as well as in reagents, medidna]
preparations, and foods, the following tests are employed. The first two are
modifications of the Marsh test; but all have the advantage over the Marsh
test in that they are more rapid and require no special apparatus.

3. The Ontxeit Test for arsenic depends upon the &ct that arsine color? a
solution of silver nitrate (l : l) first yellow and finally black. To carry out
this test, put in a test tube a few pieces of arsenic-free zinc and cover with
about 3 cc. of dilute sulphuric acid. Place near the top of the tube a plug of
cotton, stopper the lube with a loosely fitting cork which has been covered
with 2 folds of filter paper moistened with AgNO, solution (1 : i), and allow
to stand several minutes. If no darkening of the paper is produced, the blank
is satisfactory. Now remove the plug and stopper, and introduce a very smalt
amount of the solution or substance to be tested for arsenic. Replace the
plug and stopper, and allow to stand again for several minutes. A yellow
stain which quickly becomes black proves the presence of arsenic Fre-
quently, especially with solutions of silver nitrate less concentrated than 1 ; I,
the yeUow stage is not seen. The reactions involved are the following : —

(1) 6 AgNO, + AsH, = I Ag^ ■ 3 AgNO, -I- 3 HNO, ;

(2) Ag^ - 3 AgNO, -1- 3 H,0 = H^O, -I- 3 HNO,-f |6 Ag.

Phosphine, stibinc, and hydrogen sulphide interfere with this reaction ; the
last can t>e guarded against by moistening the cotton plug with lead acetate
solution. Instead of AgNOg, HgO, may be used ; this yields a yellow stain.

3. Fleltmann Test. As the Gutzeit test does not distinguish between arsenic
and antimony, Fleitmann devised a method by which the arsenic alone can be
detected. This consists in generating the arsine in an alkaline solution.

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so QUAUTATIVB CHEMICAL ANALYSIS

Method. Into a test tube place a small piece of arsenic-free Zn or Al ;
cover with a few cubic centimeters of NaOH and heat to boiling to start the
reaction, then remove from flame, add the arsenic solution, cap with stopper
covered with paper mobtened with silver nitrate solution, and allow to stand ;
a blackening proves the presence of arsenic. If the arsenic is in the pentad
state, it should fiist be reduced with SO, bdbre applying this test.

4. Bettendmiri Teat depends upon the fact that in a solution strongly add
with hydrochloric add, stannous chloride reduces arsenic ccmpounds to
metallic arsenic : —

3 AsCl, + 3 SnOj = 3 SnCl, + ^ 2 As.

The test b carried out as follows : To 3 cc. of concentrated HCl in a test
tube, add i cc. of strong SnO, solution ; then add a few drops of the solution
to be tested for As and heat gendy. A brown color or predpitate indicates
the presence of arsenic. Antimony b not reduced under these conditions.
The addition of a small piece of tin foil will have the effect of hastening the
reaction, but must not be used if bismuth or antimony b known to be present.

J. Belnach Tect. If a solution containing arsenic, to which \ of its bulk .
of concentrated HCl has been added, b boiled with 3 strip of bright copper
foil, the latter becomes coated with a gray deposit of copper arsenide (CujAsj) .
If the foil is removed, washed, and dried between the folds of £lter paper, and
then slowly and carefully heated in a dry test tube, a white crystalline subli-
mate of As,Oj wiU form ; the latter can readily be recognized by examining
with a lens or confirmed by dissolving in boiUng water and applying the
Fleitmapn test.

SeniltlTenesa of the Special Arsenic Tests
Harsh test will detect i part of As in 200,000,000

Gutzdt test will detect r part of As in 10,000,000

Bettendorif test will detect i part of As is 7,000,000
Reinsch test will detect i part of As in 40,000.

Any solid substance containing arsenic, when mixed intimately
with four times its weight of a mixture of KCN and Na,COg,
and heated in an ignition tube, will yield a black mirror of
metallic arsenic on the cooler part of the tube. The sensitive-
ness of this test is i part in 8000.

Oxidation of arsenious to arsenic compounds can be accom-
plished by the addition of iodine ; the reaction proceeds best in
a solution alkaline with sodium dicarbonate : —

KHjAsOb -I- NaHCOg + Ij = Nal + KI + 1 CO, + HgAsO(.

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TBE METALS $1

Reactions of Arsenic Compounds

1. NaOH, KOH, NH4OH or Na,CO, produces no precipitate.

2. Hydrogen Solphlde. From cold, moderately acid solu-
tions of arsenic acid, HgS precipitates, after some time, a mix-
ture of AsaSg + S. The H,S first reduces the arsenic acid with
the separation of sulphur, and then precipitates AsgSg readily
from the reduced arsenic (-ic) solution : —

(i) H8As04-|-H3S=HaO + |S + H8As08;
(2) 2 Hj AsOg + 3 HaS = I AsjSg + 6 H3O.

If the arsenic solution is heated, the reduction and precipita-
tion are hastened. If the amount of HCl is considerable, the
stream of HjS rapid, and the solution cold, all of the As will be
precipitated as AsjSj : —

2 HbAsO, + 5 HjS = 8 HjO + +As,Sj.

When, under the same conditions of acidity, the solution is
heated and then treated with a rapid stream of HjS, a mixture
of AsjSa and AsjSg is obtained.

To rapidly precipitate the arsenic existing in the pentad state,
it should be first reduced by adding sulphurous acid (HjSOg) to
the cold solution and boiling till the excess of SO^ is expelled.*

From the resulting reduced solution, HjS will rapidly precipi- .
tate the arsenic as As^Sj : —

HgAsO, + HiSOg = HaSOi + HgAsOs !■

AsgSg has the same solubility as As^Sg ; it dissolves in
(NHj)jS with the formation of ammonium tbioarsenate, from
which HCl reprecipitates AsjSg : —

AsaSe + 3(NH^)aS = 2(NH4)a ASS4 ;
2(NH4)gAsSt-|-6HCl = |AsjSs+6NH4CI + t3HjS.

* The reduction is best accomplished by adding the HiSOa to the cold solution
contained in a piesiuie bottle, stoppering, and heating in a boiling water bath for
one hour. The bottle should be thorooghl]' cooled before opening.

t If alksMne earth caetaU are present, they will be predpitaled by the H1SO4
formed.

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52 QUAUTATIVE CHEMICAL ANALYSIS

3. Silver Nitrate precipitates from strictly neutral solutions
chocolate-colored Ag3As04 (distinctioii from arseuious and phos-
phoric acids) : —

3 AgNOg + NagAsO^ =| Ag^O, -I- 3 NaNO,.
The precipitate is easily soluble in acids and in ammonium
hydroxide,

4. Magnesia mlztore yields (better when the solutions are
cold) with neutral or ammoniacal solutions a white crystalline
precipitate of NH4MgAs04{distinction from arsenious acid): —

K8A'sd]|+ MgClj+ NH,Cl = |NH4MgAs04+ 3 KCL
The precipitate is soluble in acids, but insoluble in 2.5 per cent
ammonia water.

5. Ammonium Holybdate, when added in great excess to a
hot nitric acid solution of arsenic acid, yields a yellow precipi-
tate of ammonium arsenomolybdate of variable composition
(distinction from arsenious acid): —

HjAsO, + i2(NH,)aMo04 -I- 21 HNOg =

12 HaO + 21 NH^NOg -f- 4(NH4)gAs04 ■ t2 MoOg.
The presence of NH^NOj favors this reaction. The precipitate
is soluble in ammonium hydroxide, also in an excess of HaAs04;
hence the necessity of having an excess of the reagent. Phos-
phates, or phosphoric acid, give a precipitate of similar appear-
ance, hence they should be absent in making the test

6. Reducing Agents, like FeSO,, HjSOb, NaaSOg, when boiled
with a solution of an arsenate strongly acid with HCl, reduce
the substance from the arsenic to the arsenious state.

Any arsenic compound, when treated with strong HCl and
distilled in a current of HCl gas, will yield a distillate of AsClg.

Potassium Iodide, when added to an acid solution of HgAsO^,
will reduce it to HaAsOj with the separation of iodine : —

HbAsOj + 2 hi = HgAsOa -f- HjO + 1 la-
This test serves to detect arsenic acid in the presence of arse-
nious acid.

Special Tests for the Detection of Small Amoonts. In the
Marsh and Gutzeit tests, the reduction to AsHg takes place les&

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TEE METALS 53

rapidly, due to the necessity of a preliminary reduction of
H^OjtoHjAsO,: —

HgAsO, + H, = HgAsO, + HjO-
With the Fleitmann test, preliminary reduction with H)SO| is

Antimony

Like arsenic, antimony forms two series of compounds, viz.,

antimonic salts, in which antimony acts as pentavalent; and

antimonious compounds, in which antimony behaves as a trivalent

element.

Reactions of Antimonious Compounds

In carrying out the following reactions a hydrochloric acid
solution of SbClg may be employed.

I. Sodium Hydroxide, Ammonium Hydroxide, and Sodium Car-
bonate each precipitates white antimonious hydroxide, Sb(OH)g,
insoluble in ammonium hydroxide, but soluble in an excess of the
fixed caustic alkalies and in a hot solution of alkali carbonate : —
SbClg + 3 NHpH = \ Sb(OH)a + 3 NH,C1;
SKOH)s + 3 NaOH = Na,SbOa + 3 HjO.
NajSbOj readily hydrolyzes in contact with water, yielding
sodium metandmonite, NaSbO,: —

NaaSbOg + HjO = 2 NaOH + \ NaSbO,.
The latter is further hydrolyzed by water, yielding finally white
SbjO,:— 2NaSbOa+H,0 = 2NaOH + |Sb,08.
SbgOg is practically insoluble in water and in nitric acid, but
readily dissolves in hot concentrated HCl with the formation of
SbCls-

Tartaric acid and the tartrates dissolve it in accordance with
the following equations: —

SbjOg + 2 HjC^HjO, = 2 H(SbO)C4H^Oe + HjO ;
SbjO, + 2 KHCjH^O, - 2 K(SbO)C4H,Oe + H,0.

Tartar euutic

In both of the resulting soluble compounds of antimony, the
group (SbO), called antimonyl, acts as a monovalent radical
similar to (NO), nitrosyl, in nitrosyl sulphuric acid, H(N0)S04;

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54 QVAUTATIVE CHEMICAL ANALYSIS

tartar emetic may, therefore, be called potassium antimonyl tar-
trate. Ttie solubility of antimony compounds in tartaric acid is
of great analytical importance.

2. Water. If to a soludon of SbClg containing not too much
free acid a relatively large quantity of water is added, there
forms a white precipitate of antimony oxychloride, SbOCl: —

SbCla + HjO -Z I SbOCl + 2 HCl.
As indicated, the reaction is reversible, too much HCI having
the effect of reversing the reaction ; precipitation may be has-
tened by heating. The precipitate is easily distinguished from
the corresponding bismuth compound by its solubility in tartaric
acid: —

SbOCl + HaQHp, = H(SbO)C4H40s + HCl.

The precipitate is also soluble in strong HCl and can be changed
directly to Sb^Sj by HjS: —

2 SbOCl + 3 HjS = |Sb,S|, + 3 HjO + 2 HCl.

3. Hydrogeo Sulphide. From solutions not too strongly acid
with HCl, HjS precipitates red SbjSg: —

2 SbCIg + 3 HaS^lSbaSg + 6 HCL
The reversibihty of the reaction indicates that a high concentra-
tion of HCl would prevent the precipitation, also that the pre-
cipitate when formed would dissolve in strong HCl. It has
been found by experiment that HCl (i : i) readily dissolves Sb^Ss
(distinction and method of separation from As). S\S^ is solu-
ble in (NH4)aS with the formation of a thio salt: —

SbjSs-H 3(NH,)aS = 2^(NH^^b^^^^

If yellow (NHj)3S is used, the excess of sulphur in the latter
oxidizes the thioantimonite formed in the last reaction to thio-
antimonate : —

SbaSj ■¥ 3 (NHj)aS. = 2 (NH^^jSbS^ -H (3 a: - 5)S.
The great similarity of the chemistry of the thio salts of anti-
mony and arsenic is thus seen.

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TBE METALS 55

If the solution of SbjSg in (NH4)aS, — that is, the solution
containing ammonium thioantimonate and an excess of (NH4)^Si
— is acidified with HCl, we get (as with the As compound) the
higher sulphide precipitated and at the same time a separation
of sulphur resulting from the decomposition of the excess of
(NH,)aS.:-

2 (NH4)3SbS4 + 6 HCl =|SbaS, + 6 NHjCl + 3 HjS ;
(NH4)jS. + 2 HCl = 2 NH^Ci +tH,S +|(jr - i)S.

The sulphide of antimony is also soluble in alkalies, from solu*
tions of which HCl reprecipitates SbgSg.

4. Zn-Pt Couple. If a solution of antimony, acid with HCl, is
poured into a dish containing a piece of platinum foil and a
piece of zinc is added so that it touches the platinum, there will
form on the platinum foil a black deposit or stain of metallic
antimony. Even in dilute solutions this characteristic test can
be applied. If arsenic is known to be present, the test should
be carried out under a hood because of the possible formation
of arsine.

5. If a solution of antimony, acid with HCl, is heated with a
bright iron nail, all the antimony will he deposited in the form
of black flocks (distinction from Sn).

Antimonic Compounds

I. Water. If a solution of SbClj, not too strongly acid with
HCl, is diluted with a relatively large amount of water, a white
precipitate of SbOjCl is fopned : —

SbClj + 2 HjO ^^ SbOaCl + 4 HCl.

If the dilution is very great, the SbO,Cl is further changed to
antimonic acid : —

SbOaCI + 2 HaO ^IHgSbO^ + HCL

As with SbOCI, tartaric add prevents the precipitation of
SbOjCL

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S6 QUALITATIVE CHEMICAL ANALYSIS

2. Hydn^en SnlpUde. From moderately add solutions of
SbClj, HjS precipitates orange-red SbjSg : —

2 SbCIg + S HjS =+SbjSj + 10 HCl
The precipitate is soluble in concentrated HCl wiUi the forma-
tion of SbCls and evolution of HjS : —

SbjSg + 6 HCl = 2 SbClfl +i 3 HjS +\2 S.
It possesses the same solubilities as the trisulphide, dissolving
in (NH4)aS with the formation of ammonium thiantimonate,
(NH4)BSbS4; on acidifying the latter with HCl, the pentasul-
phide is reprecipitated : —

2 (NH4)BSbS4 + 6 HCl "ISbaSj + 6 NH^Cl H-f 3 HjS.
SbgSg also dissolves in caustic alkalies.

3. Potassiain Iodide, when added to a HCl solution of SbCl,,
reduces it with the separation of iodine [distinction from Sb
(-ous) compounds] : —

SbClg + 2 KI = 2 SbClg + 2 KCl +|I,.

Special T«ats for Small Amonnta of Antlmonj

I. TheHarali Teat. This is carried out in the same manner as directed
for arsenic. The stibine (SbHg) which forms is decomposed in the hot tube
with the separation of metallic antimony in the form of a black mirror which
is insoluble in a solution of NaBrO (distinction from As).

SbH, is further distinguished from AsH, by the formation of black Ag^b
when the former is passed into a solution of silver nitrate : —

SbH, + 3 AgNOs = 4- SbAg, + 3 HNO,.
With AsHj the black deposit is due to metallic silver (see p. 49).

a. Gutzeit Test. Same as for As, the blackening being due to AgjSb.

3. The Selnach Test, when applied to antirnony compounds, yields a black
coating on the copper foil, which, when dried and ignited, gives a non-crystal-
line sublimate of Sb,0,. The latter is insoluble in water but is soluble in x
hot solution of KHCjHjOj, from which H^ precipitates red Sb^,.

Neither Fleitmann's nor Bettendoiff's test are applicable to antimony
compounds.

TiK

The two oxides of tin, SnO and SnOj, correspond to two
classes of salts known respectively as the stannous and statmic

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THE METALS 57

compounds. In the former, tin is divalent ; in the latter tetra-
valent

Reactions of Stannous Salts
The stannous salts are all colorless. Those which are solu- -
ble in water yield solutions which have an acid reaction ; the
solid salts as well as their solutions rapidly absorb oxygen from
the air with the formation of stannic compounds.

1. Sodium Hydroxide, Ammonium Hydroxide, or Sodium Car- .
bonate gives a white precipitate of Sn(OH)g, which is readily
soluble in excess of NaOH with the formation of sodium stan-
nite ; it is insoluble in excess of the other precipitants.

SnCL, + 2 NaOH = |Sn(OH)j + 2 NaCl;
Sn(OH), + 2 NaOH = Na,SnOj + 2 H,0.

The precipitate also dissolves in HCl. It possesses, like
A1(0H)8, both acid and basic properties; substances of this
character are called amphoteric substances.

2. Hydrogen Sulphide. From moderately acid solutions (con-
taining not more than 2.5 per cent, of concentrated HCl) HgS
throws down a brown precipitate of SnS: —

SnCl3-f-HjS = |SnS-l-2 HCL

SnS is soluble in strong HCl (distinction from As), nearly in-
soluble in colorless (NH4)3S [distinction from the sulphides of
As, Sb, and Sn (-ic)], but is soluble in hot (NHj)jSi: with the
formation of ammonium thiostannate, from which HCl precipi-
tates yellow stannic sulphide, SnSg : —

SnS -I- (NHj)aS- = (NH^)aSnSB + (.r-^S;

3. Mercuric Chloride, when added in excess to a solution of
SnCl^ is reduced to white insoluble HgCl ; the SnCl^ is oxidized
at the same time to S11CI4 : —

2 HgCI, -t- SnCl, = ^2 HgO -H SnCI,.

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58 QUAUTATIVE CHEMICAL ANALYSIS

If, however, tfae SnClj is present in excess, the HgCl first
formed is further reduced to metallic mercury (gray or black): —

2 HgCl + SnCl, = I 2 H|+ SnClf

As this reaction is essentially one of reduction, it is important
that the HgCl, solution contain no oxidizing agent Stannic
compounds do not give this reaction ; it thus serves to distin-
guish stannous from stannic compounds.

4- Bismuth salts are reduced by an alkaline solution of stan-
nous salts with the precipitation of black metallic bismuth (see
under Bismuth, reaction 4).

5. Metallic Zinc. When metallic zinc is introduced into
a hydrochloric acid solution of either SnCIj or SnCIj, metallic
tin is precipitated on the zinc in the form of a gray spongy mass.
As the deposited tin is readily soluble in strong HCl, care must
be taken not to have the solution too strongly acid.

SnCl4-t-2 Zn=!2ZnCL,-|-|Sn;
SnClj -I- Zn = ZnCla + ^ Sn.

Stannic Compounds

With the exception of the sulphide all the stannic compounds
are either colorless or white. They are generally obtained from
stannous salts by oxidation ; thus, a solution of SnCl4 for the
following tests may be prepared by warming a rather strong
HCl solution of SnClj, with KCIOg added in small portions, until
the solution becomes yellow, and then boiling oS the excess of
chlorine ; after a slight dilution with water, the solution is ready
for use.

Reactions of a Solution of SnClf

I. Sodinm Hydroxide, Ammonlam Hydroxide, as well as Sodltun
Carbonate, yield a white precipitate of stannic hydroxide,
Sn(0H)4, which, on drying, becomes HjSnOg. The precipitate
is soluble in excess of NaOH or Na^COs with the formation of
sodium stannate of variable composition.

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THE METALS 59

3. Hydrogea Sulphide. From moderately acid solutions not
exceeding 2.5 percent, concentrated HCl, H,S precipitates yellow
SnS,: —

SnClj + 2 H,S = ^, SnS, + 4 HCL

SnSa is readily soluble in HCl (l : i), hence the necessity for
having the solution not too strongly acid. The disulphide of
tin readily dissolves in colorless (NH4)jS (distinction from SnS)
, with the formation of ammonium thiostannate, from which
HCl precipitates SnS, (yellow) : —

SnSj + (NH4)jS = (NH4),SnSg;
(NH4),SnS8 + 2 HCl = 2 NH^Cl + f HjS + ISnSj.
On strong ignition in the air, SnS, is quantitatively converted
into SnO,.

3. Hercuric Chloride gives no precipitate witlt stannic salts
(distinction from stannous).

4. Hydrochloric or sulphuric acid does not precipitate stan-
nic salts from solutions that are moderately concentrated (dis-
tinction from metastannic compounds); when, however, the
solutions are diluted and boiled, a precipitate of Sn(0H)4 is
obtained : —

SnCl* + 4 HjO :^| Sn(0H)4 + 4 HCl.

5. Potasdam or Sodium Snlphate. From cold solutions no
precipitate is obtained with these reagents (distinction from
metastannic compounds); but, on boiling, a precipitate of
Sn(OH)4 is obtained.

Reactions 4 and 5 can be explained on the assumption that
the oxy-salts of stannic tin first form, but being unstable in
dilute solutions are decomposed into stannic hydroxide, thus: —
(i) SnCl4+2 HaS04=Sn(S04)j + 4HCI;

(2) Sn(S04)j + 4 H,0 = 2 HjSO, + ^SnCOH),.

Similarly, with K^SOj =- we get

SnCl4+ 2 K,S04= Sn(S04)j + 4 KCl,
the Sn(SOi), being then hydrolyzed as shown' above in
equation (2).

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6o QVAUTATIVE CHEMICAL ANALYSIS

Metastannic Compounds
There arc two forms of stannic compounds ; vii., the normal and the
metastannic forms. The normal may be considered as derived from stannic
hydroxide, formed by the action of NaOH on SnCl^. It is readily soluble
in adds. The metastannic compounds are derived from metastannic acid,
a white substance obtained by the action of hot dilute HNO, on metallic tin ;
it has the same empirical formula as the partially dehydrated Sn(OH)j, i.t.,
HjSnO^ but differs from it in being insoluble in acids. When boiled for a
short time with concentrated HO, a compound of the formula Sn,OjCIj(OH)g
forms which, though quite insoluble in HCl, is readily soluble in water. From
the fact that this and similar compounds may be formed from metastannic
add, the formula Sn,0,(OH)ia or 5 (H^nOj) has been assigned to it.
Stannic hydroxide, when dried over concentrated H,SO^ has the formula
H^SnOf ; metastannic add is thus seen to be a polymer of stannic hydroxide.

Reactions of Metastannic Chloride, Sn^0^Cl4fiH\

1. HCl precipitates Sn60,Cl4(OH)g, 4 HjO.

2. Prolonged boiling with water causes the precipitation of
all the tin as metastannic acid, insoluble in dilute acids.

3. H^SOj, KaS04, or Na2S04 precipitates a white substance
which changes, 00 washing with water, to metastannic acid
(distinction from stannic chloride).

4. KOH precipitates metastannic acid, which is converted
by an excess of the concentrated reagent to a potassium salt ;
the latter is soluble in water and in dilute KOH solution.

5. NH4OH precipitates metastannic acid.

6. H2S yields the same precipitate as with SnCl^ solutions.
Solutions of stannic compounds are converted into the meta-
stannic form by diluting and boiling : —

S SnCl4 + 13 HjO^ 18 HCl + SngOjCI^COHV
Conversely, metastannic compounds are converted into the
stannic form by boiling with concentrated HCl or concentrated
KOH.

Action of HaS

Besides its action as a group reagent for predpitating the metals of Group

II., HjS also acts as a redudng agent. Should, therefore, an oxidiung agent

be present in the solution subjected to the action of H,S, it will be reduced,

the HjS being oxidized at the same time to elementary sulphur, which sepa-

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THE METALS 6i

lates ia a finely divided state, and, in some cases, partlj to sulphuric add.
Among the oxidizing agents likely to be present in the filtrate from Group 1.
are FeO,, K,CtjO„ KMnOj, HNO3, and aqua regia. The reduction of the
first three substances is accompanied by a chaise in color of the solution,
thus fi^quendy affording an indication of their presence. For example, a
solution containing ferric salts undergpes a change from a yellow or reddish
yellow to a colorless condition — 2 FeCI, + HjS = 2 FeCl, + 2 HQ + + S ; a
K,Cr,Or solution changes by the action of H2S from reddish orange to green
— KiCr,0, + 3 H^ + 8 HQ = 2 CrOj + 2 KQ + 7 H,0 + 1 3 S ; while a so-
lution containiug KMnO^ changes from a solution with purple tint to one that
is colorless : —

1 KMnO, + 5 H^ + 6 HQ = 3 MnQ, + 3 KCl + 8 H,0 + 1 5 S.

Should the concentration of nitric acid be large, it will oxidize the H^
with separation of sulphur and partly with the formation of H^SO^: —
2 HNO, + 3 H,S = 4 HjO + -t2NO + |3S;
3H,S + 8HN0, = 3H^O,+|8NO + 4H,0.

Aqua regia will oxidize the HjS in accordance with the equation —
Cl,+ HiS = 2Ha + |S.

It will be observed that in every case the presence of an oxidizing agent
causes the decomposition of the H^ with the separation of S ; with a. Large
amount of oxidizing agent present, the amount of S and M^O^ will be
formed in quantity sufficient to seriously interfere with the analysis. A large
quantity of sulphur is undesirable because it complicates and masks the results;
and the presence of H,SO, will have the effett of precipitating the alkaline
earths along with the metals of the second group, so that where the amount
of oxidizing agent is large it is advisable to eliminate the latter before pass-
ing in HgS. If, from the purple or orange-red color of the solution, KMoO,
or VLjZtfij is suspected, reduction may be readily effected by acidifying with
HCI, adding alcohol, and boiling. For most purposes, it will only be neces-
sary to consider the presence of a large excess of HNO, or aqua regia, be-
cause of their extensive use as solvents.

An excess of HNO, is removed by evaporating the solution to about I cc,
adding 3 cc of concentrated HCI, and evaporating nearly to dryness. It can
then be taken up with the aid of HQ and hot water.

An excess of aqua rigta is disposed of by boiling the solution down to a
small bulk, adding concentrated HCI and again evaporating to I cc. ; it 13
then diluted with water and a few drops of HCI.

H,S aa a PredpltatiDg Agent. In precipitating the second group sulphides
with H,S, it Is exceedingly important that the solution have a certain approxi-
inately definite acidity. If too great a concentration of add is present, com-
plete predpitation will be impossible, owing to the appredable solubility of
some of the sulphidea in moderately strong HCI (notably those of Pb, Cd,

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62 QUAUTATIVE CHEMICAL ANALYSIS

and Sn). On the other hand, if the acid concentiatton is too small, certain
metals of the third group will also precipitate, 9Zn, Ni, and Co.

By experiment it has been found that a c^centiation of 2.5 cc. of HC]
(sp. gr. 1.2) in a volume of loo cc. affords a satisfactory additj for the
sepai^on of the second and third groups by H^.

Predpltatloii vitb H^S

The filtrate (i) from Group Lis made slig-Atfy aXkahae -miii
■NH^OH and then j'usi acid with dilute HCl (2); 2.5 cc. of
concentrated HCl are then added, the solution is heated nearly
to boiling and is treated with a rapid stream of HgS for a few
minutes. Without filtering (3), add enough cold water to make
the total volume 100 cc, cool to room temperature, and pass in
HjS again unti! precipitation is complete. Filter, dilute the
filtrate with ^ its volume of water, and treat again with H^S ;
now filter off any precipitate formed (4). The final filtrate
should not give a precipitate when treated with HjS. The
beaker containing the filtrate should be labeled Groups III.-V.,
at once placed on a wire gauze, and boiled until all the H^S is
expelled (5).

The precipitate may consist of HgS, PbS, Bi^Sg, CuS, CdS,
AsjSb. SbgSa, SnS and S ; it should be washed with water con-
taining HjS and about s per cent. NH^NOg (6) until the wash-
ings are only faintly add. Reject the washings.

ITOTBS

1. A preHminaiy test for the second group should first be made on a small
portion of the filtrate, in order to determine whether or not Group II. is
present. If present, the entire filtrate should be treated with H^ in accord-
ance with directions; if absent, the introduction and removal of H^ will thus
be avoided. In that case pass to Scheme III.

2. The solution must be thoroughly stirred with a glass rod during the
addition of the ammonium hydroxide and add, and the acidity or alkalinity
of mixture determined by means of litmus paper and not by the quantity of
the reagent added. No attention need be given to precipitates which form,
because these are either finally dissolved or converted by H„S into sulphides.
If a large excess of add is known to be present, it should be removed by
evaporation and the solution then brought to the proper condition of addity
as directed in the procedure above.

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THE METALS 63

3. The solution is not diluted at once to 100 cc. because of the possible
presence of arsenic, which comes down best in a hot strongly acid solution.
It b a good plan to marlcf with a kbel the level at which the beaker will hold
100 cc. ; the dilution can then be made without resorting to a measuring
cylinder.

4. The color of the H,S predpitate sometimes affords an indication of the
metals present. If blade, it may be due to Pb, Cu, Hg, or to all of them ; if
yellow, to Cd, SD(-ic), or As; if orange, to Sb. A ydlon precipitate
which is insoluble In (NH,),S, cannot be anything other than Cd ; on the
other hand, if the yellow predpitate dissolves completdy in (NH^^,, it must
be either the sulphide of As or Sii(-ic), or both.

5. As H3S in solution readily oxidizes in contact with air to S and HjSO„
and as the latter will precipitate alkaline earths, the necessity for immediately
expelling the HjS is apparent.

Keeping a glass rod in the beaker during the boiling will fadlitate tbe
removal of H^ by preventing dangerous bumping, with a consequent loss of
liquid. The completeness of the expulsion of the H^ may be determined by
holdingapieceof filter paper moistened with lead acetate in the escaping vapor.

6. The precipitate is washed with HjS water to prevent the oxidation
of the sulphides to sulphates, which, with the exception of PbSO„ are all
soluble in water. NHjNO^ is added to prevent the precipitate from going
into the colloidal state and then passing through the filter.

The separation of Group II. into two divisions is based on
the difference of behavior of the sulphides towards (NH4)jSi.

Division II. Aj|the copper group) includes those sulphides
which are insdlmie in (NH j)jSi ; these are Hg, Fb, Bi, Cu, and
Cd.

Division II. B (the tin group) includes those sulphides which
are soluble in (NH4)jSj with the formation of thio salts. The
separation, however, is not sharp, which is due to the slight
solubility of CuS in (NH4),S,. CuS is practically insoluble
in NajSp but the latter quite appreciably dissolves HgS. For
all practical purposes, the separation with (NH^^jS^ is suffi-
ciently complete.

In the analysis of the HgS precipitate it is sometimes just as
well to assume the presence of both divisions and to treat the
well-wasked precipitate at once with (NH4)jS„ as directed in
paragraph 3. In most cases, however, it is preferable to make
the following prelimioary tests.

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64 QUAUTATIVE CHEMICAL ANALYSIS

Preliminary examination of the H^S precipitate to determine
the presence of —

(r) Division A (copper group). By means of a glass spatula,
put a very small amount of the precipitate into a small evapo-
rating dish; add about 15 drops of (NH^jjS^ diluted with an
equal quantity of water. Break up the precipitate with a glass
rod, and warm gently with constant stirring for a minute {do not
boil). If the precipitate completely dissolves, the Cu group is
absent and the main precipitate is analyzed for the Sn group
only (Scheme II. B). If a residue remains (i), the copper group
is present.

(2) Division B (tin group). Twice pass about 10 drops of
(NH^)jS„ diluted with an equal volume of water, through the
precipitate, which has been thoroughly washed and from which
most of the water has drained; catch the liquid which passes
through in a test tube (2) and just acidify with dilute HCl. In
another test tube,y«f/ acidify with dilute HCl an equal portion
of (NHj)5S„ diluted as above, and compare the results. A
colored precipitate in the first tube which is different from that
of the second proves the presence of the Sn group (3). If the
two tubes present the same appearance after acidification, the
absence of the Sn group is proved.

(3). Seperatioa of tbe Divisions of Group II.
If both divisions are shown to be present by the above
tests, the entire precipitate is treated in a small beaker (50 cc.
capacity) (4) with 10 cc. of (NH()jSi diluted with 5 cc. of water ;
the mixture is thoroughly stirred, warmed for several minutes,
and filtered (5). The residue on the filter may consist of HgS,
PbS, BIjSb, CuS, CdS and S- The filtrate may contain the thio
salts of As, Sb, and Sn. A warm mixture of 2 cc. of (NH4)jS,
and an equal volume of water is poured on the residue (6),
and the liquid which passes through is united with the filtrate
containing the thio salts of Division B, which is then analyzed
according to Scheme II. B. The residue is washed twice with
hot water containing 5 per cent. NH^NOg and is then analyzed
according to Scheme II. A. The washings are rejected.

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TBB METALS 65

NOTES

1. A residue <^ S is not to be taken as indicating the presence of tlie Cu
group.

2. If the precipitate has not been washed free of add, the latter will de-
compose the {NH^)^„ with the separation of S. If considerable acid is
present, all of the (NHJ^, will be decomposed, with the result that the
liquid which drains through the filter will be colorless and wilt ^ to react
with HCL To remedy this, add more (NH^),S^, preferably diluted with
NH4OH, until a colored filtrate is obtained,

3. Because of the slight solubility of Cu5 in (NHJjS^, a liver-colored pre-
cipitate is sometimes obtained in acidifying the (NHJ^S, solution.

4. If the quantity of the precipitate is small, it may be treated on the filter
with (NHj)jS„ using small portions at a time and allowing each portion to
drain through before adding a fresh portion ; in this way a maximum of ex-
traction with the minimum amount of solvent is secured. If water is used in
transferring the precipitate to a beaker, it must be carefully poured off before
adding the (NHJjS..

5. If the precipitate shows a tendency to pass through the filter in the
CoUtudal condition, add several grams of NH4NO„ warm, stir, and refilter.

6. This further treatment of the re»due with dilute (NHJ^, is given to
insure the complete extraction of the As, Sb, and Sn

Oatline at the Separatioa of the Hetals of Group n. A
Of the sulphides of Group II. A, only HgS is insoluble in
hot dilute HNOg; the addition of this reagent to the mixed sul-
phides will therefore result in the solution of all the sulphides
as nitrates, with the exception of HgS, which will be left behind
as an insoluble residue. If, now, to the filtrate containing the
nitrates of Pb, Bi, Cu, and Cd we add HaSO^, we should expect
the Pb to precipitate as PhSO^ ; for Pb is the only metal of this
group whose sulphate is insoluble in water. It is, however,
appreciably soluble in nitric acid, and as the filtrate contains an
excess of this acid, its removal is necessary if complete precipi-
tation of the Pb as sulphate is desired. This is accomplished
by adding concentrated H^SO^ and evaporating the solution
until SOg fumes appear ; it is then diluted with water and the
PbSO^ is filtered off. The filtrate will now contain Bi, Cu, and
Cd as sulphates, and an excess of HjSO^. A glance at the
reactions of the salts of these metals shows that NH^OH pre-
cipitates all three of them, but that Bi is the only one whose

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QUAUTATIVE CHEMICAL ANALYSIS

hydroxide is insoluble in excess. If, therefore, an excess of
NHjOH is added to the filtrate from the PbS04, Bi(OH)8 will
be precipitated and may be separated from the remaining two
metals by filtration. The ammoniacal filtrate will be colored
blue if Cu is present Cu and Cd may be separated by taking
advantage of the difference of behavior of their double cyanides
towards H^S. The double cyanides are formed by adding KCN
to the ammoniacal solution until the blue color is discharged;
the passage of H,S into this solution precipitates only the Cd as
yellow sulphide.

SCHEME n. A

The residue from the (NHJ^Sj treatment may consist of HgS, PbS, fiijS^

CuS, and CdS. Wash the precipitate into a small beaker, pour off the water,

add 15-30 CC. of dilute HNO„ and heat with constant stiiriog (l) ; txul for

one and a half minutes, and £lter.

Beaidne may be
HgS (black) or
2 HgS ■ Hg(NO,),
(white) + S (2).
Wash with water.
Transfer ppt. to a
small evap. dbh ;
add 4 CC. aqita rt-
gia, and boil till
all but S dissolves.
B(h1 a little longer
to espel O, dilute
with I CC. of water,
and filter. To fil-
trate add a few
drops of SnCl^; a
white ppt.y turn-
ing gray to black,
proves the pres-
ence of Hg.

Filtrate may cont^n Pb(NO,)p Bt(NO,)^ Cu(NO0»
Cd(NO^, + excess of HNOg. Transfer to an evap. dish,
add 5 CC of cone. H^SO,, and evaporate under a hood until
SO, fumes are given off (3) ; cool and cautiously p>our the
contents of dish into a beidcer containing 35 cc- of water.
Rinse what remains in the evap. dbh with a little water
into the same beaker; stir, allow to settle, and filter.

Sestdneis
PbS04(4). Wash
once with water,
and treat the ppt.
the filter with
CC. of a b
ing solution

NH.CsHiOj
Catch filtrate i
test tube, add z cc.
acetic acid and

K,CrO,.
yellow ppt. CO I
firms the presence
ofPb.

FUtiaU contains Bi,(S04)„ CuSO„
CdSOj + excess of HjSO,. AddNH(OH

to alkaline reaction and then in slight
excess. A deep blue coloration proves
the presence of Cu (5). Allow any
ppt. which forms at the same time to
settle and filter.

BMidue b
Bi(OH), (6).
Wash with water;
c^ssolve ppt. on the
filter with about
5 drops of cone.
HCl, and catch
drops in a clean
beaker. Add ;o cc.
of water, warm, and
allow to stand for
a few minutes; a
white ppt. or doudi-
neas is BiOa (7).

Filtrate contaios
Cu(NH,),SO^,
Cd(NHs)4SO, +
excess of NH,OH.
Add KqN until the
solution is decolor-
ized, and pass in
H^. A yellow ppt
is CdS (8).

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THE METALS

I n. A

1. Stirring while heating witb dilute HNO, u important because of the
tendency of the S, which separates in a plastic condition, to indoae portions
of the sulphides, with tlie result that the latter are protected from the solvent
action of the add.

2. Besides the substances mentioned, the residue ma; consist of a little
PbSO, resulting from the oxidation of PbS by the use of strong HNOj or the
long-coDtinued action of the dilute add. But, as FbSO, is somewhat soluble
in hot dilute HNO„ enough Pb passes into solution for its detection in the
next operation.

A black residue is not to be taken as proof of the presence of Hg ; it may
be sulphur mechanically indosing small quantities of the blade sulphides, as
PbS, CuS, and Bi^,. Consequently the residue after the HNO, treatment,
whether it is black or white, must be tested for Hg.

3. The object of evaporating the solution until SO, fumes result is to com-
(detely remove the HNO„ which has a solvent action on the PbSO^. As the
boiling point of concentrated HNO, is I30° C- and the fuming point of H^O^
is 250° C, it is evident that all the HNO, will have been removed when
the solution is boiled until dense white fiimes of SOg are given off. The
student should not look for SO, fumes until the bulk of his solution has been
reduced to atwut 3 cc. If he is unable to recognize these fiimes with certainty,
he should show hb results to his instructor before proceeding with the next

'-fltep. Unless thb operation is properly conducted, it will not be possible to
completely separate the Pb, with the result that the tests for Bi and Cd will
be interfered with.

4. PbSOj is a heavy white powder; a white coarsely crystalline pred^
tate (a basic sulphate of Bi) sometimes separates, hence the necessity of
making a confirmatory test for Fb. Where the amount of PbSO^ b ver7
small, it can be made dbtincUy vbible by coUectiag it in the center by means
of a rotary motion imparted to the beaker,

5. The deep blue solution produced by an excess of ammonium hydroxide
is suffidently sensitive for the detection of Ca, A much more delicate lest
consbts in addifying a portion of the solution with acetic add and addii^
K^e(CN),; a brown predpitate or coloration proves the presence of Cu.

6. The formation of a white predptate at this point Is not proof of the
presence of Bi ; for if all the Pb had not been removed in the previous opera-
tion it will predpitate h^. A confinnatoiy test for Bi most therefore always
be made.

7. It frequently happens that a pred[ntate ot doudiness is not obtained
even when Bi b present. Thb b due to the presence of an excess of add,
which reverees the direction of the reaction : BiO, + H,O^BiOa + 2 HO.
Thb may be remedied by adding MH^OH drop by drop to nentcalize the
eiKxas oi »<Ad, tart iamfftaiat, however, to keep the solutwiKidd.

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68 QVAUTATIVE CHEMICAL ANALYSIS

Another confinnator)' test for Bi consists in poaring on the thoroughly
washed white precipitate of Bi(OH)( a solution of Na^aOj (prepared bj add-
ing NaOH to I cc. of SnCI^ till the precipitate which first forms dissolves),
when if Bi is present it will be blackened due to the precipitation of metallic Bi.

8. The presence of Hg or Pb in the solution to be tested for Cd will yield
a black precipitate wbeo H^ is passed into the solution. A little Hg may
find its way into the solution if the original H^S precipitate had not been
thoroughly washed free from HCl or chlorides'; the latter, on boiling with
HNOg, will yield agua regia, which dissolves some of the HgS. The
presence of Pb is due to its incomplete removal in the previous operation. A
black precipitate obtained with HjS, in testing for Cd, may be examined for
this metal by filtering the precipitate, thoroughly washing it with hot water,
and finally Jreating it with hot sulphuric acid (i pt. of cone, acid to 4 pts. of
water) 00 the filter. The dilute H^SO^ dissolves the CdS and leaves on the
filter the HgS and PbS ; the latter may be entirely changed to PbSO^. If the
filtrate is now largely diluted with water and treated with H^S, a yellow pre-
dpitate of CdS will be formed if Cd is present.

Outline of the Analysis of Gronp II. B (the Tin Group)
The insolubility of AsjSs in hot concentrated HCl is made
use of to separate if from the sulphides of Sb and Sn ; the
latter two dissolve in this acid, forming the corresponding
chlorides with an evolution of H^S. The residue, after filtra-,
tion, is taken into solution with concentrated HNOj; and the
presence of arsenic, now in the form of arsenic acid, is con-
firmed by its precipitation with AgNOj in a neutral solution as
AggAsOj. When the AsaSj is removed by filtration, the filtrate
will contain the Sb and Sn as chlorides and an excess of H^S.
As the tests for Sb and Sn can be made in the presence of
each other, it is needless to effect their separation. The filtrate,
after boiling to expel the HjS, is divided into two portions.

An iron nail is placed in the first portion and the liquid
warmed. The u-on acts on the acid present, liberating hydro-
gen, which reduces SnCl^ to SnCL, and at the same time pre-
cipitates the Sb in the metallic state. The filtered solution,
containing SnClg, is then tested with HgCI, solution.

The second portion is tested for Sb by the galvanic action of
the electric couple (Pt and Zn), which causes the antimony to
precipitate as a black deposit on the platinum.

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TBE METALS 69

SCHEME II. (TIN OROVP)

The filtrate 6btained after treating the H^S precipitate with
(NH4)gS, will contain the thio salts of the metals of this group;
viz.,(NH4)8AsS4.(NH4)8SbS4,(NH,),SnSg and exces3(NH4),S,.
yarf acidify with dilute HCl (i) and filter; reject the filtrate.

The residue will consist of AsjSj, SbjSj, SnSj, (CuS ?), and S.

Transfer the precipitate to a small beaker, add ro cc. of con-
centrated HCl, and heat gently to boiUng (2), with constant stir-
ring, for about 5 minutes. Dilute with an equal volume of water
and filter.

ftMldue is As,S, + 5 (3}. Wash with Iiot
water until the washings after boiling to expel
HjS give only vl faint reaction with AgNOj.
Reject washings. Transfer ppt. to an evap.
dish (if water is used in transfeirlDg ppt.,
pour it off after ppt. settles). Add 3-5 cc.
of cone. HNO^ stir, and heat gently until do
more brown fiimes are given otT, and until the
excess HNO, is expelled. Dilute with 3 cc.
of water and filter through a small filter.
Wash filter with i cc. of water, catching
filtrate and washings in a test tube. Add
5 cc. of AgNO, (4) ; filter if a precipitate
forms. To the clear solution or filtrate add
one drop of phenolphthalein and then render
just alkaline with NHpH. Now add 5 %
acetic acid drop by drop with shaking until
theresolting mixture is bintly add. A choco-
late-colored ppt. of Aj^AsO^ confirms the
presence of arsenic (5).

Filtrate may contain SbCl„
SnCl, + excess HQ -^ H^.
Boil until the H^ is com-
plettfy expelled (6). Divide
the solution into 3 portions.
In the 1st portion, test for Sn
hy warming vn^ an iron nail
for 3 minutes. Filter rapidly
(7) into a test tube containing
2-3 drops of HgClj ; a white
ppt., which may turn gray or
black, proves the presence of
Sn. In the znd portion, test
for Sb. Pour it into a small
evap. dish containing Pt foil in
contact with a piece of Sn or
Zn. A black st^n on the Pt
(8), which is insoluble in
NaBrO, is Sb.

ROTES TO SCHEME IL B
L. An excess of add is to be avoided because of the solubility of SnS, i
n moderately dilute add.

3. The separation of As from Sb and Sn sulphides by the use of hot con-
centrated HCl is not always vety sharp. With mixtures consisting of a small

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yo QUAUTATIVB CHEMICAL ANALYSIS

amount of As and a relatively large quantity of Sb, the insoluble residue nuy
contain enough Sb^S^ to give it a red color; thereforeared residue must always
be examined for As.

4. If all the HQ had not been removed by washing, the addition of AgNO,
will yield a white precipitate of AgCl ; if this precipitate is large in amount,
more AgNO, should be added before filtering to insure an excess of the latter
in the filtrate.

5. The test for arsenic with AgNO, depends upon the formation of
AggAsO,, which only forma in a strictly neutial solurion ; if too much aceric
add is added, precipitation will Ml, because of the ready solubility of Ag^AsO^
in adds as well as in alkalies. To remedy this, carefully neutralize the excess
of add by the addition of dilute NH,OH.

6. Test escaping vapors with lead acetate paper.

7. By this procedure the SnCl^ is reduced to SnCl,; as the latter ra^dly
oxidizes on exposure to air, particularly in a hot solution, the necessity of
ra^ndly filtering into a test tube containing the reagent is apparent.

6. If much Cu and little or no Sb are present,a dark red stain, easily dis-
tinguished from a black stain, will be produced.

The deanlng of the Pt foil b easily accomplbhed by first washing it witk
water and then pouring on it concentrated HNOj.

Reacdons of ICetals of Group ni
The metals of this group are distinguished from those of tfie
first and second groups by the fact that they accnot precipitated
by HjS from solutions containing 2.5 per cent of hydrochloric
acid, sp, gr, 1.2. They are associated together in one group be-
cause of their common property of being completely precipitated
by (NHj)jS in solutions alkaline with ammonium hydroxide in
the presence of NH^Cl (distinction from Groups IV. and V.).

Aluminum

The aluminum salts are nearly all colorless ; the salts of the
halogen adds, and the nitrate, sulphate, and acetate, are soluble
in water.

I. Ammonium Hydroxide throws down a white gelatinous
precipitate of Al{OH)g, slightly soluble in excess; on boiling,
the dissolved hydroxide is reprecipitated. The presence of

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THE METALS 71

NH4CI diminishes the solvent action of ammonia on the hydrox-
ide; hence, to completely precipitate aluminum by ammonia,
the latter should be added only in slight excess and the mixture
boiled until the liquid has but a faint odor of the reagent.
When freshly precipitated, A](OH)g is readily soluble in
acids : —

AlClg + 3 NHjOH = if Al(OH)8 + 3 NH^Cl ;
Al(OH)g + 3 HCl = AlClg + 3 HjO.

Aluminum hydroxide is also soluble in caustic alkalies (see 2).

3. Potasslnm or Sodinm Hydroxide precipitates A1(0H),,
soluble in excess with the formation of alkali aluminate: —

AlCOH), + 3 NaOH = NajAlO, + 3 HjO.

On carefully neutralizing the alkaline solution of sodium
aluminate with hydrochloric acid, Al(OH)g is reprecipitated : —

{a) NagAlOs + 3 HCl = 3 NaCl + \ A1(0H),.

If an excess of acid is added, the precipitate which first forms
is dissolved and we obtain : —

(*) Al(OH)i, + 3HCl=AlCl8+3HaO.

It is evident that if the original sodium aluj^ioate solution is
at once acidified with HCI, we shall get the net result of (a) and
{b). Adding {a) and {b), and eliminating A1(0H)3, which ap-
pears on opposite sides, we get: —

NajAlOg -1- 6 HCl = AlClg -J- 3 NaCl + 3 HjO.

If, now, we heat this solution to boiling and add ammonium
hydroxide in faint excess, all the aluminum will be precipitated
as the hydroxide : —

AlClg + 3 NHjOH = 4. AI(0H)8 -J- 3 NH^CL

While the addition of a large excess of solid NH4CI will have
the effect of precipitating Al(OH)g from the aluminate, the
above process, viz., that of acidifying first with HCl and then
rendering the resultiDg solution faintly alkaline with ammonium

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73 QUAUTATIVE CHEMICAL ANALYSIS

hydroxide, is the more common procedure and the one to be
generally recommended.

It is important to remember that the direct additioa of am-
monium hydroxide to a sodium aluminate solution will not pre-
cipitate Ai(OHV

^^"3. Ammoniam Sulphide precipitates AI(OH)g and not the
sulphide. AljSg may be prepared in the dry way, but, on bring-
ing it in contact with water, it at once hydrolyzes with the for-
mation of the hydroxide and the evolution of H^S. The action
of (NH4)jS on solutions of aluminum salts may be represented
as taking place in two steps: —

(a) 2 AlCIg H- 3(NH4)jS = AljSs -f- 6 NH^O;
{b) AljSg -H 6 HjO = 1 2 A1(0H)8 H- 3 H,S.

Adding {a) and {b), and eliminating Al^Sg, we get as the equa>
tion for the final result : —

2 AlCla-f 3(NH^)aS -H 6 HjO = +2 AK0H)8 -H 6NH^C1 + 3 H,S.

4. Sodiam Carbonate also precipitates Al(OH)g.

In the presence of non-volatile organic acids, as tartaric, citric,
and malic acids, as well as certain organic matter containing
(OH) groups, as aygars and starch, ammonium hydroxide, sodium
carbonate, and ammonium sulphide fail to precipitate aluminum
salts.

5. Alkali Acetate. If an excess of alkali acetate is added to
a slightly acid or neutral solution of an aluminum salt, and the
mixture is largely diluted with water and boiled, a bulky pre-
cipitate of basic aluminum acetate will be thrown down: —

AlCl, ■¥ 3 NaCaHgO, = AI(C,H30a)8 + 3 NaCl ;
Al(C,Hg03)3 -I- HjO :5^ ; AKOHXCjHgOj), -t- HCjHgOa

The reagent is, in fact, hot water, which hydrolyzes the weak
salt Al(CaH80j)g. Cooling the solution, or the presence of an '
excess of acetic acid, will have the effect of reversing the re-
action, with the result that some of the precipitate will dissolve.

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THE METALS 73

6. Slsodinm Phosphate yields with solutions of aluminum salts
a gelatinous precipitate of AlPO^, soluble in HCI and NaOH,
but insoluble in acetic acid : —

(i) NagHPOi + AlClg = I AlFOj + 2 NaCH- HCI ;

(2) NajHPO, + HCI = NaHjPO, + NaCL
Adding (i) and (2), and eliminating HCt, we get : —

(3) 2 NaaHPO^ + AlClg = | AlPO^ + NaHaPO, + 3 NaCl ;
(a) AlPO^ + 3NaOH = NasAlOa + HsPO^,

(*) HgPO, + 3 NaOH = NagPO, + 3H,0.
Adding (a) and (p), and eliminating HaPO^, we get : —
AlPO, + 6 NaOH = NagAlO, + NagPOi + 3 HjO.

7. Any aluminum compound, when strongly ignited in the
air, is converted into Al^Os; if this is moistened with a very
dilute solution of Co(N03)j and again strongly heated, a blue
mass is obtained, due to the formation of cobalt aluminate.
This reaction serves as an excellent confirmatory test for
aluminum.

Chromium
The two principal oxides of chromium are CijOj and CrOg.
The former is basic and forms the various chromic * salts by
combining with acids, e.g., Cr308 + 6HC1 = 2 CrClg+S HjO;
similariy by solution of CrjOg in H,SOj and HNOg, Crj(S04)8
and Cr(NOg)g are respectively formed. In all these com-
pounds chromium deports itself as a metal. CrOg, on the other
hand, is distinctly acid in character, being the anhydride of the
hypothetical chromic acid, HjCrO^, the salts of which are
known as chromates. The latter may be prepared by treating
CrOg with a base ; thus, sodium chromate (Na^CrOj) may be
prepared by treating CrOg with caustic soda : CrOg + 2 NaOH
= NajCrO^ + HjO. In the chromates, chromium plays the

* In tfait case the ending -ic lefeis to the element when acting u a base, i.i., its
electco-poaitive propettiet dominate. This majr perhaps beat be shown by the
valence ai Ci'", chromic, etc.

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74 QUAUTATIVE CHEMICAL ANALYSIS

part of the acid radical CrOf, the reacdoas of which are dififer-
ent from those given hy Cr when a constituent of a chromic
salt. An example will serve to illustrate this difference.
Ammonium- hydroxide, when added to a chromic salt, hke
CrClg, causes a precipitate of chromium hydroxide to form ;
when added, however, to a chromate, as Na^CrO^ no precipi-
tate results. Further, if to chromic chloride we add a solution of
barium chloride or lead acetate, no precipitate results ; while if
the same reagents are added to sodium chromate, yellow pre-
cipitates are formed, due to the formation of BaCrO^ and
PbCrOj, respectively.

The distinction is further noted when we compare the aque-
ous solutions of chromic salts and chromates ; the former pos-
sess a green or violet color, while the latter are nearly always
yellow.

Chromic salts (Cr™) are converted into chromates (Cr''^) by
oxidation in an alkaline solution ; conversely, chromates (Cr^')
are reduced to chromic salts (Cr"') by reduction in an acid
medium.

The essential change may best be seen by considering only
the oxides as taking part in the reactions ; * thus, the oxidation
of a chromic salt to a chromate is given by the equation

CrjOj +30 = 2 CrOg,

while the reduction of chromate to a chromic salt may be repre-
sented by

2 CrOs -t- 6 H = CrjOg + 3 HjO.

{a) Oxidation of Chromic Salts to Chromates. The oxidation
is always carried out in an alkaline medium. In the dry way
the oxidation may be accomplished by fusing a chromic com-
pound with a mixture of Na^COg (which supplies the alkali)
and an oxidizing agent like Na,Og, KClOg, or KNOg (which

* Ai all chromic lalts nu^ be dcTived from CrtOg b^ treatment of the latter with
the appropriate acid, And as the valence of Cr is the lamein this oxide aod its salts
we ma; conveniently repteeent all chromic witi in oiiddRon equations bji CrgOa-
FoT a similar reason, all chiomatei may be represented in reduction reactions by
CtOt.

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THE METALS 75

supplies the O). Id its simplest form the equation for the
oxidation is —

CrjOa + 3 Na^COg + 30 = 2 Na^CrOj + f 3 CO,.

The oxidation may be carried out in an alkaline solution by
using any one of tbe many oxidizing agents, such, for instance,
as Br (or any halogen), KMnO^ or H^Oy The alkali first pre-
cipitates chromic hydroxide : —

CrClg + 3 NaOH = | Cr<OH)g + 3 NaCl.
This then dissolves in excess, giving sodium ckromite : —

Cr(OH)s+ 3 NaOH = NaBCrOj + 3 H,0.
Tbe chromite is then oxidized by the oxidizing agent to chro-
mate: —

2 NaaCrO, +'3 6,4- H^O = 3 NajCrO^ + 3 NaOH.

When sodium dioxide (NajO,) is used, it is needless to first
make the solution alkaline, because the sodium compound in
contact with water is decomposed, yielding NaOH and O,
according to the equation

NajOa + H3O = 2 NaOH + O.
An excess of NajO, will therefore yield the excess of NaOH
necessary to convert the chromic salt to sodium chromite, while
tbe oxygen Uberated at the same time will oxidize the chromite
to chromate : — . ■' ,

2 NagCrOg + 3 NajOj + 4 HjO - 8 NaOH + 2 NajCrO^.

Tbe oxidation by means of sodium dioxide is to be prpfeired
to the other agents for the conversion of chromic compounds
to chromate. In every case the oxidation is accompanied by a
change in color from green to yelldw.

If a solution of a chromate is acidified, the color changes from
a yellow to an orange-red, due to the formation of a dichro-
mate; —

2 K,Cr04 + 2 HNOg = KjCrjO^ + 2 KNOg -f H,0.

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76 QUALITATIVE CHEMICAL ANALYSIS

Conversely, if a base is added to a dichromate solution, the color
changes from orange-red to yellow, due to the formation of a
chromate : —

KjCrgOj + 2 KOH = 2 KgCrO, + HaO.

Both chromates and dichromates, when in solution, may be
precipitated by solutions of Ba or Pb salts [distinction from
chromic (Cr"") compounds] : —

KaCrOj + PKCaHsOa), = | PbCrO^ 2 KCaHgOa ;
KjCrjO, + 2 BaClj + Hp = 1 2 BaCrO^ + 2 KCl + 2 HCI.

(d) Redaction of chromates to chromic compounds is effected in
acid solutions by any one of the many reducing agents, e.^.,
HjS, HI, SOj, concentrated HCI, and various organic sub-
stances, as alcohol and oxalic acid.

With concentrated HCI the reaction is —

KjCrjOT + 14 HCI = 2 KCH- 2 CrClg + 7 HaO + f 3 Cly

With HjS the reduction takes place in accordance with the
equation

KaCraO, + 3 HjS + 8 HCI = 2 CrClg + 3 KCl + ; HjO + 1 3 S.
In this case the green solution appears turbid from the separa-
tion of S.
With sulphurous acid the equation is —

KaCrjOj + HaSO^ -I- 3 HjSOb = Cra(SO,)B -I- KjSO^ -I- 4 HjO.

In all the above cases the reduction is evidenced by a change in
color from orange-red to green.

Other reaction for chromates will be given in Part II., dealing
with the acids (see page 142).

TAe Chromic Salts

Of the common salts of chromium, the sulphate and the

chloride exist in two forms : one is very readily soluble in water ;

while the other, which has been ignited, is neither soluble in

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THE METALS 77

water nor acids. The nitrate exists in one form only and is
easily soluble in water. All aqueous solutions of chromium
salts have either a green or violet color, which varies with the
concentration and other conditions. A solution containing as
little as r part of chromium in 10,000 parts of water will have a
distinct bluish green color.

Reactions of tke Chromic Salts

1. Anunoniam Hydroxide produces a greyish green or blue
gelatinous precipitate of Cr(OH)}, soluble with difficulty in
excess with the formation of a violet solution, from which, on
boiling, Cr(OH)g is reprecipitated. The precipitate is easily
soluble in acids and in sodium hydroxide (see 2).

2. Sodium or Potasslom Hydroxide precipitates Cr(OH)g, solu-
ble in excess in the cold to a green solution with the formation
of sodium chroraite ; on boiling this solution, Cr(OH)B is repre-
cipitated (distinction from AI). The precipitate is easily solu-
ble in acids.

CrClg + 3 NaOH = | Cr(OH)a -f 3 NaCl ;
Cr(OH)j, -I- 3 NaOH = Na^CrOg + 3 Hp ;
NagCrOg -H 3 HjO (boiling) = | Cr(OH)g + 3 NaOH ;
Cr(OH)g-t-3HCl = CrClg-H3HaO. .

3. Ammonium Sulphide precipitates Cr(0H)3, for Cr,Sg, like
AJjSg, is hydrolyzed by water with the formation of Cr(OH)g
and the evolution of HjS : —

2 CrClg + 3(NH^)jS -|- 6 HjO =

1 2 Ci<OH)b -H 1 3 HjS + 6 NH^Cl.

4. Sodium Carbonate also precipitates the hydroxide. The
presence of non-volatile organic acids, like tartaric and citric
acids, as well as organic matter containing (OH) groups, as sugar
and starch, interferes with reactions l, 2, 3, 4, and 5.

5. Dlsodium Phosphate precipitates from solutions of chromic
choride green CrPO^ : —

2 NaaHPO, -H CrClg = 3 NaCl -H NaHjPOi -I- ICrPO^.

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78 QVAUTATIVE CHEMICAL ANALYSIS

The precipitate is easily soluble in inorgaaic acids, but is prac-
tically insoluble in cold dilute acetic acid, although it is soluble
in a targe excess of 50 per cent acetic acid.

6. Sodium Dioxide, If a solution of a chromic salt is treated
with a sufficient amount of sodium dioxide and boiled, all of the
chromium will be converted into sodium chromate. The reac-
tion may be represented by the following equations : —

(i) 3 NajOa + 3 HgO = 6 NaOH + 3 O ;

(2) CrCls + 6 NaOH = NagCrOg + 3 NaCl + 3 HjO ;

(3) 2 NajCrOg +30 + HjO = 2 NaaCrO^ + 2 NaOH.

7. If Sodium Acetate is added to a solution of a chromium salt,
no precipitate is produced even on boiling. If, however, the
solution contains relatively large amounts of iron (ferric) and
aluminum, the chromium will be almost completely precipitated
as a basic acetate on boiling (compare the corresponding reac-
tion for aluminum). Should the iron and aluminum be present
in small and the chromium in relatively large amounts, the pre-
cipitation will be incomplete and in the filtrate will be found
some of the Al, Cr, and Fe.

The important deduction from these facts is, that in the pres-
ence of a large amount of chromium it is necessary, in order to
completely precipitate aluminum and iron as basic acetates, that
one of the latter metals be present in large excess.

Iron
Iron, as an electro-positivtf' element, forms two distinct classes
of salts 1 viz., the ferrous compounds, in which iron is divalent,
and the ferric salts, in which iron is trivalent. As the two
classes exhibit a difference in behavior when treated with the
same reagents, we shall consider them separately.

The Ferrous Compounds

When they contain " water of crystallization " the ferrous

salts are green, and when anhydrous, they are white. The

aqueous solutions, except when concentrated, are almost color-

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TBE METALS 79

less. FetTous salts in soluBoD are very unstable, for they rapidly
absorb oxygen from the air and are converted into basic ferric
salts, difficultly soluble in water. Oxidizing agents readily change
ferrous salts to ferric compounds.

Reactums

1. Amnumltun, Sodium, or Potassium Hydroxide precipitates
at first white gelatinous Fe(OH)3, which, on exposure to the air,
is rapidly oxidized, becoming first dirty green, then black, and
finally a reddish brown; the last is ferric hydroxide, and the
other colors are doubtless due to varying mixtures of ferrous
and ferric hydroxides.

FeCL+ 2 NH.OH =iFe(OH)a+ 2 NH.CI;

WHlle

2 Fe(OH)s + O + HjO = 1 2 Fe(0H)8.

Beddlab brawn

In the presence of much ammonium chloride, ammonium hy-
droxide fails to yield an immediate precipitate ; but on exposure
of the ammoniacal solution to the air, ferric hydroxide is finally
thrown down. If the air is excluded, ammonium hydroxide
does not precipitate ferrous salts in the presence of a sufficient
quantity of ammonium salts (distinction from ferric salts).

The property of not being precipitated by ammonium hydrox-
ide in the presence of a sufficient amount of ammonium salts is
not peculiar to ferrous salts alone, but is shared alike by the
salts of nickel, cobalt, manganese, zinc, and magnesium.*

2. Hydrogen Snlphide, in acid solution, gives no precipitate.
From neutral solutions a slight precipitate of FeS results ; if,
however, considerable sodium acetate is present, a larger, though
still incomplete, precipitation is obtained. From alkaline solu-
tions, HgS completely precipitates the iron as black ferrous
sulphide.

* An eiidatution of this bet zexy be found in the Tktery ef EUttrelyHt Dissoei-
■atien wad the Law a/Mast ActUm. The presence of NH4CI diminiihei the concen-
tration of the (OH) ioni derired from the ammoniiun hydroxide to neh ui extent u
to yield with the ferroni iroD preient an ■mount of Fe(OH)i leu than the lolabilitr
product of the ktter.

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So QUAUTATIVE CHEMICAL ANALYSIS

3. Ammoniam Sulphide precipitates black FeS, easily soluble
in acids with the formation of a ferrous salt and evolution of
HaS : — pgcij + (NH4)aS = | FeS + 2 NH^Cl ;

FeS + 2 HCl = FeClj + f HaS.
When moist, it readily oxidizes in the air, becoming first ferrous
sulphate and finally brown basic ferric sulphate. To prevent
this oxidation, the precipitate should be washed with water con-
taining ammonium sulphide. The presence of ammonium chlo-
ride assists the precipitation.

4. Potaasium Cyanide precipitates brown ferrous cyanide,
soluble in excess with the formation of potassium ferrocya>
nide : — p^^l, + 2 KCN = | Fe(CN)a + 2KCI;

Fe(CN)j-J- 4 KCN = K^Fe(CN)g.
The solution of potassium ferrocyanide does not give any of the
reactions of ferrous salts ; it is therefore not a ferrous salt, but
the potassium salt of ferrocyanic acid, H4Fe(CN)8. The group
Fe(CN)g is an acid radical like CrO^ in chromates and differs
distinctly in its behavior from iron, existing as the simple metallic
component of salts.

5. Potassium Ferrocyanide precipitates, in the complete ab-
sence of air, white K,Fe"Fe(CN)g ; under ordinary atmospheric
conditions, however, a light blue precipitate is obtained, due to
partial oxidation ; on prolonged exposure, it is completely con-
verted into a dark blue precipitate of prussian blue : —

FeCIa + KjFeCCN), = | FeKjFe(CN)8 + 2 KCL

6. Potassium Forricyanide produces even in very dilute solu-
tions of ferrous salts a dark blue precipitate, known as TumbuU's
blue, which is indistinguishable in color from prussian blue : —

3 FeCla-H2 K8Fe(CN)B = |Fe8[Fe(CN),]2-f6 KCl.
The precipitate is insoluble in HCl, but is decomposed by caustic
alkalies with the formation of ferrous hydroxide and alkali ferri-
cyanide : —

Fe8[Fe(CN)e]a + 6 KOH = | 3 Fe(OH)j-|- 2 KgFe{CNV

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THE METALS 8i

The fenicyanide at once oxidizes the ferrous hydroxide, so that
the final products are Fe(OH)8 and K4Fe(CN)g.

7. Potassinm thlocTanate gives no reaction with ferrous salts
(distinction from ferric salts).

Oxidation of Ferrous to Ferric Salts. It has been already
stated that solutions of ferrous salts are very unstable, oxidizing
gradually on exposure to air to ferric compounds. The oxida-
tion can be more rapidly accomplished by the use of oxidizing
agents in acid solution, as the halogens, aqua regia, a mixture of
HCl and KClOg, nitric acid, potassium permanganate, potassium
dichromate, and hydrogen dioxide. The equations for the oxi-
dation of ferrous salts by nearly all of these oxidizing agents
have been given under Oxidation and Reduction (see page 25).

In oxidizing with nitric acid, the strong acid should be added
drop by drop to the boiling acid solution of ferrous salt until no
furt^r darkening of the solution is evident. The oxidizing
action of hydrogen dioxide and aqua regia, respectively, may be
represented by the following equations : —

2 FeCl, -1- 2 HCl-t- HjO, = 2 FeCIg + 2 HjO ;
3FeCla+3HCl + HN08=3FeCl8 + tNO+2H,0.

Ferric Salts
Most of the ferric salts, as the chloride, nitrate, and sulphate,
yield solutions with a yellowish brown color, which varies in
intensity with the concentration and temperature of the solution,
as well as with the quantity of free acid present. The ferric
ammonium alum, Fej(S04^ • (NHj)jSOt ■ 24 HjO, is violet.
Ferric salts in dilute aqueous solutions are readily hydrotyzed,
particularly on heating, with the formation of an insoluble basic
ferric salt which dissolves on the addition of an acid : —
Fes(S04)B + HjO ^1 Fes(SO,)aO + H^SO,.

I. Ammonlam, Sodlnm, or PotasBlom HTdroxUe precipitates a
reddish brown gelatinous precipitate of FetOH),. The predpi-

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82 QUAUTATIVE CHEMICAL ANALYSIS

tate is unaffected by the presence of ammonium salts [distinc-
tioQ from Fe(OH)j], and is soluble in acids, but is insoluble in
an excess of sodium hydroxide (distinction from Al and Cr) ; it
is also insoluble in an excess of ammonium hydroxide: —
FeClg + 3 NH^OH = |Fe(OH)g + 3 NH^Cl;
Fc(OH)g + 3 HCl = FeClg + 3 H,0.

On ignition it yields FcjOg : —

2 Fe(0H)8 + (heat) = FCjO, + 3 H,0.

Ignited, Fe,Og is difficultly soluble in dilute acids, but dissolves
on prolonged treatment with hot concentrated hydrochloric acid.

3. Ammonlom Sulphide gives with acid solutions a precipitate
consisting of FeS + S. From ammoniacal solutions, black ferric
sulphide, FejSg, is precipitated : —

2 FeClj + 3 (NH4)jS - + FejSa + 6 NH^Cl.

The precipitate is readily soluble in hydrochloric acid with the
formation of ferrous chloride and the separation of sulphur : —

FeaSg + 4 HCl = 2 FeClj + 1 2 H,S + |S.

3. Potassium Ferrocyanlde produces with ferric salts a blue
precipitate known as prussian blue : —

4 Fed, + 3 K,Fe(CN)9 = +Fe4[Fe(CN)g], + 12 KCL

The precipitate is insoluble in dilute HCl, but dissolves in
oxalic acid, as well as in a great excess of the precipitant, with
the formation of a blue solution. Prussian blue is decomposed
by caustic potash, the products being ferric hydroxide and
potassium ferrocyanide : —

Fe4[Fe(CN)fl]g + 12 KOH = U Fe(OH), + 3 K,Fe(CNV

In making this test for iron, it is important that the solutions
contain only a small amount of strong add, as the latter would
parti^y decompose the reagent with the formation of a small
quantity of iron salt, which, reacting with the unchanged portion

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THE METALS 83

of the reagent, would yield a blue coloration. Neutral solutions
containing i part of iron in 500,0CX) parts of water will give this
reaction. When only small amounts of iron are present, a blue
or green coloration, instead of a blue precipitate, is obtained.

4. Potassium Fenicranlde does not precipitate ferric salts,
but produces a brown coloration (distinction from ferrous salts).

5. Potassium Thiocyanate gives with solutions of ferric salts
a deep red coloratiqp, due to the formation of ferric thiocyanate,
which is soluble in water : -=-

FeCIa + 3 KCNS^Fe(CNS)8 + 3 KCL

The reaction being reversible, its sensitiveness is increased by
adding an excess of the reagent. As little as i part of iron in
1,600,000 parts of water can be detected by this reagent; The
dehcacy of the test may be further increased by adding a little
pure ether and shaking ; the ether extracts, and thus concen-
trates, the colored body. Nitric and chloric acids also give with
the reagent a red coloration, but the latter, when due to these
substances, is destroyed by adding alcohol and heating. Rela-
tively large amounts of alkali acetate, organic acJds, like tartaric,
acetic, and oxalic, as well as phosphoric, arsenic, and boric acids,
interfere with the reaction in neutral, though not in strongly
acid, solutions. The addition of acid in making the test is
therefore advisable. Mercuric chloride bleaches the red color-
ation.

6. Dlsodlom Hydrogen Phosphate in neutral or slightly acid
solutions of ferric salts containing a relatively large amount of
sodium acetate, produces a buff-colored precipitate of ferric
phosphate : —

(a) FeClg + 2 NajH PO, =| FePO, -I- NaHjPO, -I- 3 NaCl ;

(b) FeClg + NaaHPO, + NaCaHgOj

=^FePO^-t- 3 NaCl -|- HC,Hg(\

In (a) all the iron is precipitated but not all the phosfihoric
add ; in {b) both the iron and phosphoric add are precipitated.

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84 QVAUTATIVE CHEMICAL ANALYSIS

FePOj is insoluble in acetic acid, but readily dissolves in HCL
Caustic alkalies decompose it into Fe(OH)g and NagPOj : —

FeP04 + 3 NaOH =| Fe(OH)B + NaaPO^.
Treatment with ammonium hydroxide or hot water effects a par-
tial hydrolysis into the hydroxide.

7. Sodium or Ammonlam Acetate, when added in excess to a
slightly acid solution of a ferric salt, causes the solution to take
on a reddish brown color, due to the formation of ferric ace-
tate:—

FeClg + 3 NaCjHgOa = Fe(CaHgOj)a + 3 NaCL

If this solution H largely diluted and boiled, all the iron will be
precipitated as a basic acetate : —

Fe(CaH80a)8 + HaO(boiling):^|Fe(OHXCjHaOa)a +HCaH80a.
The presence of non-volatile organic acids or sugar interferes
with the precipitation of Fe in reactions r, 6, 7.

8. Reduction of ferric salts to ferrous may be readily effected
in acid solution by reducing agents, as HjS, nascent H, SnCl,,
HaSOg, HI, and others. The following equations illustrate
this: —

2 FeClj, + HaS =2 FeCla+ 2 HCl +\S ;

FeCIg + H (from Zn + HCl) = FeCIa + HCl ;

2 FeClg + SnCla = 2 FeClj + SnCl^ ;

3 FeCIj + HaSOg + HjO = 2 FeClj -I- 2 HCH- HaSO^ ;
FeClg+HI =FeCla+HCl-l-|I.

Nickel
When in the crystalline condition or in aqueous solutions, the
nickel salts are green ; when anhydrous, they are yellow. The
green solutions can be rendered colorless by admixture with
cobalt compounds in the proportion of 3 of nickel to i of cobalt.
I. PotaBsium or Sodium Hydroxide precipitates green gelati-
nous Ni(OH)j, insoluble in excess and not oxidized on exposure
to air : —

NiCla + 2 NaOH =|Ni(OH)a + 2 NaCl.

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TBE METALS 85

The predpitate is readily soluble in acids ; also in ajnmonium
hydroxide and ammonium salts. If the alkaline solution con-
taining Ni(OH)j in suspension is treated with bromine or
chlorine and the mixture boiled, black nickel (-ic) hydroxide is
formed : —

Ni(OH)j + NaOH + Br=|Ni(OH)s+ NaBr.

3. Ammonium Hydroxide, when considerably diluted and
added in small quantity, causes a green turbidity, due to the
formation either of a basic salt or the hydroxide : —
NiClj + 2 NH^OH = I Ni(OH)a + 2 NH^CI.

The precipitate is readily soluble in excess or in the presence of
ammonium salts, with the formation of a blue solution contain-
ing a nickel ammonia salt : —

Ni(OH)a + 2 NH^Cl + 2 NHg = NiCNHsXCIj + 2 H,0.
Therefore, in the presence of sufficient ammonium salts, Ni is
not precipitated by ammonium hydroxide.

3. Hydrogen Sulphide yields no precipitate in solutions of
nickel containing mineral adds or much acetic acid. If, how-
ever, the acetic acid solution contains a relatively large amount
of sodium acetate, or if the solutions are rendered ammoniacal,
hydrogen sulphide will completely predpitate the nickel as black
nickel sulphide : —

NiCla + 2 NaCaHaOa -|- HjS = | NiS + 2 NaCl -t- 2 HCjHgO^

4. Ammonium Sulphide gives with neutral or alkaline solu-
tions of nickel salts a black precipitate of NiS, somewhat soluble
in excess, espedally in the presence of free ammouia, with the
formation of a dark brown solution (distinction from Co). If
this brown solution is acidified with acetic add and boiled, NiS
is repredpitated. The presence of large quantities of ammo-
nium salts prevents the solution of NiS in (NH4)3S solution.

NiCl, -f- (NHi)3S= I NiS -H 2 NH4CI.

Nickel sulphide is practically insoluble in cold HCl(sp.gr. 1.02)
(distinction from the sulphides of Mn, Zn, and Fe). It is also

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86 QVAUTATIVE CSmilCAL ANALYSIS

insoluble in acetic acid, but is readily taken into solution on
heating with agua regia or concentrated nitric acid : —
3NiS + 2HNO, + 6Ha=3NiCla+f2NO + 4HjO+|3S.
The sulphur, which separates in a plastic condition, often
appears black because of the presence of some NiS inclosed in
it. If the treatment with aqua regia is continued for some time,
all the sulphide will be dissolved and the sulphur will be con-
verted into sulphuric acid : —

S + 6 CI + 4 H,0 = HjS04+ 6 HCL
On exposure to air, moist nickel sulphide is oxidized to NiSO^.

5. PotaBdnm Cyanide gives a green precipitate of nickel
cyanide, readily soluble in excess with the formation of a
double cyanide : —

NiClj + 2 KCN = I Ni(CN)3 + 2 KCl ;
Ni(CN>, + 2 KCN = K,Ni(CN)4.
If the solution of the double cyanide is made strongly alkaline
with NaOH, and then treated with bromine or chlorine and .
gently heated, decomposition of the double cyanide results with
the precipitation of black nickel (-ic) hydroxide (distinction and
method of separation from Co) : —

K,Ni(CN), + Br + 3 KOH = | Ni(OH)j + 4 KCN + KBr.

6. Potasslnni Nitrite, in dilute solutions of nickel salt3 acid
with acetic acid, gives no precipitate (distinction and method of
separation from Co).

7. Dilnetbylglyoxloie. From solutions of nickel salts, alkaline
with ammonia, an alcoholic solution of dimethylglyoxime will
yield a voluminous red precipitate of the composition shown in
the following equation : —

[CHg-C = NOH
- ' I +NiCL + 2NHa = 2NH,a

C-NOH

CH. - C = NOH CH. - C = NOv

I . I >Ni.

ICH.-C-NOH

CH, - C = NOH CH, - C » NO-

,/"

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THE METALS 87

The presence of one part of nickel in 400,000 parts of water
may be detected by this reagent Cobalt salts do not give this
reaction.

8. Borax Bead Test A borax bead, when fused with a nickel
compound in the oxidizing Same, is colored reddish brown, due
to the formation of Na5Ni(B0a)4. In the redftdng flame, the
nickel is reduced to the metallic state, imparting a gray color to
the bead.

Cobalt

The cobalt salts, when in the crystallized condition or in aque-
ous solution, are reddish pink ; in the anhydrous form, they are
usually blue. The concentrated aqueous solutions in the pres-
ence of HCl are also blue.

1. Sodium Hydroxide precipitates from cold solutions a blue
basic salt: —

CoCla -f- NaOH = |Co(OH)Cl + NaCl.
This is converted, on warming in contact with the alkali, to pink
cobaltous hydroxide : —

Co(OHX:i + NaOH = |Co(OH)a + NaCL
The precipitate is insoluble in excess, but readily soluble in
ammonium salts; hence, the presence of ammonium salts in
sufficient quantity interferes with the precipitation. On expo-
sure to the air, the pink hydroxide oxidizes to black Co(OH)g
[resemblance to Fe (-ous) and Mn, and distinction from Ni] : —

2 Co(OH)a + H,0 + O = |2 Co(OH)8.

2. Ammonlttm Hydroxide, in the absence of ammonium salts,
produces the same precipitate as in (i), but the latter readily
dissolves in excess of the reagent to a brownish solution, which,
on exposure to air or on boiling, changes to a red solution, due
to the formation of a complex ammonia compound : —

Co(OH)a + 2 NH,C1 + 2 NHg = Co(NHb)4C1j + 2 H3O.
As in the case of Al, Cr, and Fe (-ous), the precipitation of
Co as hydroxide is interfered with by the presence of non-
volatile organic acids or sugar.

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88 QUALITATIVE CHEMICAL ANALYSIS

3. Hydrogen Sulphide. Same as with NL

4. Ammonliua Sulphide precipitates in neutral or alkaline
solutions black CoS, insoluble in excess (distinction from Ni),
insoluble in HCl (sp. gr. 1.02) and in acetic acid. It is soluble
in aqua regia and concentrated nitric acid with the separation
of sulphur : —

3 CoS + 8 HN0g = 3 Co(N08), + t2 NO+4 H,0 + |3 S.

5. Potassium Cyanide gives in neutral solutions a light brown
precipitate of cobaltous cyanide, easily soluble in excess to a
brown solution with the formation of a double cyanide : —

CoCI, + 2 KCN = |Co(CN)i, + 2 KCl;
Co(CN), + 4 KCN = K4Co(CNV

The latter is similar to potassium ferrocyanide, hence it is called
potassium cobaltocyanide. On warming the solution of the
double cyanide for some time, it changes color to a bright yel-
low, due to oxidation to potassium cobalticyanide [similar to
K,Fe(CN)j,]:-

2 K,Co(CN), + HjO +0 = 2 K,Co(CN)b + 2 KOH.

The reaction takes place more rapidly if sodium hydroxide
and bromine or, what amounts to the same, NaBrO so-
lution, is added to the solution of potassium cobalto-
cyanide. Nickel does not form the corresponding com-
pound, but under these conditions it is converted into black
insoluble Ni(OH^ (distinction and method of separation
from Co),

6. Potassium Nitrite produces, when added in excess to a not
too diluted solution of cobalt acidified with acetic acid, a yellow
crystalline precipitate of potassium nitrocobaltate, KgCo(N03)^
With dilute solutions of cobalt, the mixture should be warmed
and allowed to stand for at least twelve hours in order to get
complete precipitation. The reaction may be represented as
taking place in several stages : —

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TEE METALS 89

(a) CoCl, + 2 KNOs = Co(NO,), + 2 KG ;

{b) 2 KNOi + 2 HCjHgOa = 2 HNOj + 2 KCjHgO, ;

(<r) 2 HNOj = HjO + NO + NO,;

id) Co(NOa)a + NOj = Cf^NOs),;

(«) Co(NO,)8+3 KN03 = ^K3Co(NOa),.
The precipitate is somewhat soluble in water, but is prac-
tically insoluble in a solution saturated with a potassium salt
It is insoluble in alcohol and in an excess of KNO3 solution.
Hence, for a rapid precipitation of cobalt as K3Co(NOa)B, the
solution of cobalt should be concentrated by evaporation, the
mineral acid replaced by acetic, saturated with KCl, and then
treated with an excess of KNOg solution. If the mixture is
now warmed and vigorously shaken, complete predpitatioD may
be secured in a half hour.

7. NitroBO-P-naplitliol, dissolved in 50 per cent, acetic acid,
yields with a hot solution of cobalt, preferably the chloride or
sulphate acidified with hydrochloric acid, a voluminous red pre-
cipitate of cobalti-nitroso-/3-naphthol (distinction and method of
separation from nickel, which, in HCl solution, does not give a
precipitate).

8. A borax bead, when fused with cobalt compounds either
in the oxidizing or reducing flames, is colored blue. This test
is not masked by the presence of moderate amounts of nickel.

Manganese

The manganese salts, which may be formed by the solution
of the oxide MnO in acids, are colored pink in the crystallized
condition as well as in concentrated aqueous solutions. In the
anhydrous state, with the exception of the sulphide, they are
nearly all colorless.

Reactions

I. Sodium or PotaBsittm Hydroxide produces with manganous
salts a white precipitate of Mn(OH)s, which, on exposure to air,
rapidly oxidizes, becoming brown: —

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90 QUALITATIVE CHEMICAL ANALYSIS

MnClj + 2 NaOH - 1 Mn(OH), + 2 NaCl;

Mn(OH)a + O = | MnO(OH)a (manganous acid);
MnCHOH), + Mn(OH), = I MnjOs + 2 HjO.

2. Anunoniam HTdrozide yields with manganous solutions, in
the absence of ammonium salts, a partial precipitation of white
Mii(OH)j, oxidizing, as described in ( I), to brown Mn^Og. In the
presence of a sufficient amount of ammonium salts, no immediate
precipitate forms ; but, on exposure to air, MnO(OH)j is thrown
down. The separation of manganese from any or all of the
trivalent metals of this group by means of NH4CI and ammonium
hydroxide is therefore incomplete. Non-volatile organic acids
and sugar interfere with the precipitation of Mn(OH)3,

3. Anunoniam Sulphide precipitates light pink hydrated man-
ganous sulphide, which, on exposure to air, becomes dark brown,
due to partial oxidation to MnjOg : —

MnCla + {NH4)jS = \ MnS + aq. + 2 NH^CI.

The precipitate is easily soluble in dilute acids (distinction from
Ni and Co), even in acetic acid (distinction from Zn, as well as
Ni and Co). The addition of ammonium chloride assists the
precipitation, while the presence of oxalates and tartrates retards
it. On boiling with a large excess of (NH4)3S, MnS + aq. is
changed to a less hydrated green sulphide of the formula
3 MnS . HaO.

4. Lead Dioxide and Nitric Acid. If a very dilute solution of
manganous salt, free from HCl or chlorides, is boiled with a
gram of lead dioxide and a few cubic centimeters of con-
centrated nitric acid, and allowed to settle, the clear super-
natant liquid wiU be colored purple, due to the formation of
permanganic acid : —

2 MnSO* + S PbOj + 6 HNOg

^\2 PbS04+ 3 PKNOg), + 2 HgO -I- 2 HMnO,.

This reaction is suffidentiy delicate to detect a trace of man-
ganese.

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TBE METALS gx

5. If a sodinm carbonate bead is fused with a very small
amount of a manganese compound in the oxidizing flame, or if
the fused mass, while hot, is quickly dipped into a little pow-
dered potassium chlorate, a bluish green or green mass will be
formed, due to the formation of sodium manganate, NajMnO^ : —

Mn(OH)i + (heat) = MnO + HjO ;
MnO(OH)3 + (heat) = MnO^ + HaO ;
MnO + NaaCOg + 05 = 1 COj + Na^MnOj ;
MnOj + NaCOg + O = -t COj + NajMnO,.

Zinc
Most of the zinc salts are colorless ; some are soluble in water,
and the others are dissolved by acids.

1. Sodium or Potassiam Hydroxide precipitates white gelati-
nous zinc hydroxide, readily soluble in excess with the formation
of sodium zincate [similar to Al, distinction from Fe(-ic) and
Mn]: —

ZnClj + 2 NaOH = \ Zn(OH)j + 2 NaCl ;
Zn(OH)a + 2 NaOH = NaaZnOj + 2 HjO.

Unless the solution of the zincate contains a decided excess of -
NaOH, it will he decomposed on boiling with the reprecipitatioa
of the hydroxide : —

NaaZnOa+ 2 HjO (boiling)2j2 NaOH +|Zn(OH)j.

2. Ammoolam Hydroxide yields with solutions of zinc salts,
in the absence of ammonium salts, a partial precipitation of zinc
hydroxide, readily soluble in excess in the presence of ammo-
nium salts with the formation of a complex ammonia salt : —

ZnClj + 2 NH,OH = |Zn(OH)3 -f- 2 NH4CI ;
Zn(OH)a + 2 NH,C1 + 2 NHj = Zn(NHg)4Cla + 2 HjO-

3. Hydrogen Sulphide, when passed into neutral solutions of
zinc salts of inorganic acids, incompletely precipitates white
zinc sulphide (ZnS). A partial precipitation is also obtained

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92 QUALITATIVE CHEMICAL ANALYSIS

from solutioDs containing a small amount of free mineral acid.
From solutions of zinc acetate, or from neutral solutiotis of salts
of strong acids containing a moderate amount of sodium acetate,
HjS completely precipitates all the zinc as sulphide on boiling.
Warming in the presence of alkali acetate promotes the pre-
cipitation : —

(a) ZnClj + HjS^IZnS + 2 HCl ;

(^) ZnCl, + 2 NaCaHgOj + HaS=|ZnS + 2 NaCl+2 HCjHBOa-

As ZnS is soluble in HCI, the precipitation in (a) is never com-
plete. In equation (i), NaCaHjOj has the effect of displacing
the strong HCl by the weak acetic acid, in which ZnS is prac-
tically insoluble.*

The tendency of ZnS to pass through the filter may be over-
come by precipitating the sulphide in a nearly boiling solution
of acetic acid containing a moderate excess of NaCaHgOa, and
filtering rapidly while hot. The precipitate may then be washed
with hot water containing NH^CjHgO, or NHiNOg and HjS.
Zinc may also be precipitated by HjS from sodium hydroxide
solutions : —

NaaZnO, -*- H^S = jZnS + 2 NaOH.

4. Ammoniniii Sulphide yields in neutral and alkaline solutions
a white precipitate of ZnS : —

ZnCla +(NHj),S = |ZnS + 2 mn^Cl

ZnS is readily soluble in dilute mineral acids, but is insoluble
in acetic acid and in caustic alkalies.

5. Any dried zinc compound, when moistened with dilute
cobalt nitrate solution and ignited, will yield a green mass, due
to the formation of a double oxide of Co and Zn (Th^nard's
green). This is an excellent confirmatory test for zinc and
serves to distinguish zinc from aluminum.

* For in explsnatioQ of [hii fact sccocding to Ib« ionic theorj and mast action
Utr see page 15.

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TEE METALS 93

OntUne of the Method of Analysis for Group III

From an examination of the foregoing reactions, it becomes
evident that if ammonia is added to a solution containing all the
metals of this group, in the presence of a sufficient amount of
ammonium chloride, all the trivalent metals (assuming the iron
to be in the ferric state), viz., Fe, Al, and Cr, will be precipitated
as hydroxides, while the remaining metals will be left in solution.
This method would seem a desirable one for the separation of
the third group into two divisions, and such a plan is, in fact,
adopted by some chemists. We have not adopted this method
for the reason that under the conditions given, manganese and
zinc are not completely held in solution, and if present in small
amounts may be wholly precipitated with the trivalent metals.
However, the method gives fairly satisfactory results if the
first precipitate of the hydroxides of Al, Cr, and Fe, containing
some Mn and Zn, is dissolved and reprecipitated, and the second
filtrate is united with the first

Another reaction which may be utilized in separating the third
group into two divisions is the basic acetate precipitation. This,
it will be remembered, is based on the fact that in a nearly
neutral solution containing a large excess of sodium acetate, a
large amount of boiling water precipitates the basic acetates of
ferric iron, aluminum, and chromium, while the remaining diva-
lent metals are left in solution. This method of separation, one
of the oldest in analytical chemistry, is exceedingly valuable in
some cases, but it is not to be employed as a general method,
because, as^lready pointed out (see under chromium, reaction 7),
of its uncertainty in the presence of chromium.

The method adopted in this book consists in precipitating the
entire group with (NH4)jS after rendering the solution alkaline
with NH^OH. Instead of (NH^)jS, the hot ammoniacal solu-
tion may be treated with a stream of H^S until the precipita-
tion is complete. In either case, the precipitate will consist of
the hydroxides of aluminum and chromium, and the sulphides
of iron, nickel, cobalt, manganese, and zinc. Since only the
sulphides of Ni and Co are insoluble in HO (i 19), it follows

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94 QUAUTATIVE CHEMICAL ANALYSIS

that if the third group precipitate is treated with a sufficient
amount of HCl (l : 9) and filtered, there will remain on the filter
the sulphides of Ni and Co, while in the filtrate will be found the
chlorides of Al, Cr, Fe, Mn, and Zn. The residue, consisting
of NiS and CoS, is next examined with a borax bead in the
oxidizing flame, when, if not too great an amount of nickel is
present, a blue bead will be obtained, indicating the presence of
cobalt. To separate nickel and cobalt existing as sulphides, we
must first get them into solution ; this is accomplished by heating
with agua regia, which converts the sulphides into soluble
chlorides. From the solution of the chlorides, the cobalt may
be separated from the nickel by precipitation with either potas-
sium nitrite or nitroso-|3-naphthol. The nickel in the filtrate
may be precipitated with NaOH and the resulting green hy-
droxide verified with a borax bead test. The main filtrate
contains, besides the chlorides of Al, Cr, Fe, Mn, and Zn, an excess
of HCl and H,S. The greater part of the HCl and all of the
HjS are expelled by boiling down to a few cc. It will be recalled
■that in the cold, the hydroxides of Al, Cr, and Zn are soluble
in excess of sodium hydroxide, forming, respectively, an alumi-
nate, chromite, and zincate ; while the hydroxides of Fe (-ic) and
Mn are insoluble. If an oxidizing agent like Br or HaOa is
present, the chromite is converted into the yellow chromate,
which is not precipitated on boiling. So that if a decided excess
of NaOH and a little NajO^ are added to the main filtrate, which
has been freed from HjS and the greater part of the HCl by
evaporation to a few cc, and the mixture is boiled, diluted, and
filtered, there will remain on the filter the hydroxides of Mn and
Fe C-ic), while In the filtrate we should have sodium zincate, sodium
aluminate, and sodium chromate ; the last will be evidenced by
the yellow color which it imparts to the alkaline solution. In the
residue the separation of Fe and Mn may be accomplished by
dissolving the precipitate in HCl, nearly neutralizing the solution,
and precipitating the Fe as basic acetate. From the filtrate, the
Mn may be precipitated by adding Br and boiling, or by the addi-
tion of an excess of Na^Oj or NaOH. When a rough estimation
of the amount of Mn and Fe is not desired, separation is anneces-

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TEE METALS 95

sary, for we can readily identify each in the presence of the
other. The presence of Mn may be determined by the charac-
teristic green bead it gives when a little of the mixture is fused
in a Na^COg bead in the presence of an oxidizing agent; the
iron may be detected by dissolving part of the precipitate in hot
dilute HCl and adding a few drops of potassium ferrocyanide,
when a blue precipitate of prussian blue will be obtained. The
filtrate from the Mn and Fe precipitate will contain sodium chro-
mate, sodium aluminate, and sodium zincate, as well as an excess
of NaOH. If this solution is acidified with HNOj, about three
grams of NH^Cl are added, and then it is rendered slightly alka-
line with ammonium hydroxide, only the Al will be precipitated.
The zinc does not precipitate because of the presence of NH^Cl,
while the chromium no longer acts as metal but as the acid
radical (CrO,), and in consequence is not precipitated by am-
monium hydroxide. The filtrate from the A1(0H^ will contain
zinc, chromium, and a slight excess of ammonia. By rendering
the solution acid with acetic acid and adding BaCl,, all of the
chromium will be precipitated as BaCrO^. From the filtrate '
the Zn may be precipitated by HjS.

Scheme of Analysis for Group HI

This scheme is applicable only in the absence of non-volatile
organic matter and interfering acids such as phosphoric acid.

The filtrate from Group II., having been boiled to remove the
HjS, contains, besides the metals of the succeeding group, an
excess of HCl.

Preliminary Test. To a small portion of the filtrate from
Group II. which has been freed from HjS, add 2-3 drops of
concentrated HNOg and boU. Add about 0.5 g. of NH4CI and
then ammonium hydroxide to alkaline reaction. A precipitate
may be Fe(OH)a^ed). AlCOH), (white), or Cr(OH^ (greenish
blue). If the amount of Mn in the solution is large, a small
precipitate of MnO(OH), (brown) may also be obtained. If no
precipitate forms, the absence of AI, Cr, and Fe is proved. If
a precipitate is obtained, it is rapidly filtered and to this filtrate, .

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96 QUALITATIVE CHEMICAL ANALYSIS

or to the filtrate from Group II., ia which ammonium hydroxide
produces no precipitate, (NH4)jS is added ; a precipitate proves
the presence of one or more of^the remaining members of
Group III., viz., Ni, Co, Mn, andlC^ty The color of this pre-
cipitate sometimes affords an indi(iam)n of the metals present.
If it is black, Ni or Co, or both, are present ; if white, Zn is
present, and Ni and Co are absent. If pink, becoming brown
on exposure, Mn is present ; the latter may at once be verified
by the NagCOg bead + KClOa- Failure to precipitate with
NH4OH and (NH4)jS in the presence of a sufficient amount of
NH4CI proves the absence of Group III. In that case pass to
Scheme IV.

1. As a solution containing I part of Cr in 10,000 parts of water
shows a. distinct bluish green coloration, a colorless solution need not be *
tested for Cr.

2. The (NH^,S used in the preliminary testing for Group III,, as well as
that needed later in the preparation of the wash water for the Group III. ppt.,
should be nmde as needed by treating, a little dil. NH^OH with a stream of
HjS for several minutes.

3. Solutions of Ni and Co may be mixed in such proportions as to yield
an almost colorless solution; an almost colorless filtrate from the ammonium
hydroxide precipitate does not, therefore, prove the absence of Ni or Co.

SCEEBIE m
If the preliminary tests have shown the presence of Group III., the entire
filtrate from Group II. is treated with 2 grams of NH,C1 (i) rendered alkaline
widi NH,OH and then 2 cc. of strong NH,OH in excess are added (2).
The mixture is heated and treated with a stream of H^S until precipitation is
complete. Stir vigorously with gentle heating for a minute (3) and filter on
a fluted filter. [The filtrate (4) is at once made acid with acetic acid (5),
boiled until all the HjS is expelled (6), and filtered (7). The dear filtrate is
recdved in a beaker, labelled "Groups IV. and V.," covered and reserved.]
"The main ppt. may consist of A1(0H)b, Cr(OH)„ FeS.NiS, CoS, MnS, and
ZnS. Wash once with hot water containing NH,a and a Uttle (NH4)jS (8),
and discard washings. With the aid of a spatula, transfer ppt. to a beaker.
Carry to a hood and add 60-80 cc. of HCl (sp. gr. 1.02), prepared by routing
I part of cone. HCl with 9 parts of water, stir thoroughly (without heating)
for about a minute; allow to setUe (9), and filter.

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THE UETALS

Betidtie is NiS + CoS + S (lo). Wash on filter once with HO (i : 9) and
reject washings. Teat ppt. with borax bead in theO.F. A blue bead proves
the preseoce of Co. Nickel may, however, be also present (11). A reddish
brown bead proves the presence of Ni and the absence of a relatively large
amount of cobalt. In either case, transfer ppt. to a small evaporating dish,
carry to a hood, add 5-10 cc. of dil. ofua regia, and boil till all but a small
amount of black S dissolves ; evaporate /(if/ to dryness (12). Take up with
2 CC- of dil- HCl and an equal vol. of hot water; heat if necessary to effect
solution. Filter through a very small filter into a test tube. Add NaOH
drop by drop to the filtrate till a slight but permanent ppt forms. Dissolve
the ppt. in acetic acid and add about 3 cc. id excess (13).* Saturate the
solution with KQ (14) by adding the salt in small amounts and shaking
after each addition until no more dissolves. Decant the dear solution into
another test tube and to the latter add an equal vol. of KNOj. Allow the
ppt, to stand with frequent shaking for about J hour and filter. Residue is
KgCo(NOj)a (yellow). To filtrate add NaOH to alkaline reaction; a green
ppt. (15) wbich yields a brown borax bead in the 0. F. proves the presence

ofNi.

Filtrate contains A1C1„ CrClj, FeOj, MnCLj, ZnO, + HjS + excess HO.
Boil down in' a large evap. dish under hood to about i cc. (16) ; dilute with
10 cc. of water, render strongly alkaline with char NaOH solution, and add
(under hood and with caution) 3 g. of Na,0, (17). Dip finger into solution,
rub on thumb ; a greasy feel indicates solution is sufficiently alkaline ; if not,
add more NagOj. Boil with constant stirring for about i minute, add 10 cc.
of water, and filter.

*If B lolation of dimethylglyoxime is available, proceed tcata this point as fol-
lows: Divide the solution into two equal portions. First portion test for cobalt by
adding an equal volnme of KNOg solution and warming. A yellow precipitate is
K(Co(NOa)«. Confimi with borai bead. Second portion test for nickel by tendering
the lolutioa alkaline with NH4OH and adding I cc. of dimethylglyoxinie. A red
precipitate proves the presence of nickeL

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QVAUTATIVE CHEMICAL ANALYSIS

BMl(li»i9Fe(0H),
+ MnO»iH,0(i8).
Wash with hot water.
Test for Mn. On a
Na,CO, bead take
up a very small
amount of the ppt.
and heat ; while hot
dip into a little
powdered KClOj
contained in a small
watch glass. A green
or bluish greea mass
of Na^nO, proves
the presence of Hn.

Test for Fe.
Transfer part or all
of the ppt- to a test
tube, aSd dU. HO
and heat till solution
takes place. If Mn
has been shown to
be present, boil until
all the chlorine is
expelled. Cool and
add a few drops (19)
of K,Fe(CN),; a
blue ppt. proves the
presence of Fe.

FUtnte (20) may contain Na,A10j, Na^rO,, Na^ZnO,
+ excess NaOH. Render slightly add with cautious
addition of cone. HNO, ; add 3 grams of NH,C1 (zi),
heat to boiling, and then add NH^OH drop by drop
with constant stirriog until the resulting alkaline solu-
tion has only a &int odor of ammonia (22)- (If too
much NH4OH is added, boil off the excess and filter.)

SMidne

times and con-
firm by wind-

paper and ppt.,

with several
drops of
CoCNO^, (23)
and igniting
strongly. A
blue mass is co-
balt aluminate,
j-AljOj.^CoO.

FUtiat* may contain (NH(>tCr04,
Zn{NH»)4Cli + excess NH4OH. Acid-
ify with acetic acidr add a gram of
NaCjHaOj {35), and heat to boiling.
To the hot solution add BaCtj, drop by
drop, till precipitation is complete ; allow
to settle and filter through a double filter.

Keddne is
yellow BaCrOt
(24). Confinn
by treating ppt.
on filter with
hot dil. HNOb.
Catch filtrate in
a test tube. Cool
thoroughly.
Add I cc. of
ether and i cc.
39& HjO, and
shake. A blue
color in the
ether layer
proves the pres-
ence of Cr,

Elltrate, which
should be perfectly
clear (36), is treated
with HsS. A white
ppt. is ZaS (27). To
confinn the presence
of Zn, filter. Wash with
hot water, and then
moisten with 2 drops
of Co(NOii)i- Wind
Pt wire around papier
and ppt. and inciner-
ate. A green mass is
yljiO-xQaO.

1. NHtCl is added, first, to prevent Mg from predpitating with the Third
Group roetals ; second, because it aids in the predpitation aud filtration of
the sulphides by preventing them from going into the colloidal condition.

2. The solution is made alkaline with NHa to neutralize the free add. An
excess of strong NH.OH is then added to form with the HjS the (NH4)jS
which predpitates all the metals of this group. Treatment of the ammoniacal
solutiou with HiS is preferable to the use of (NHt)iS, fi>r the reason that with
the former NiS is prevented from going into solution. If, however, (NHi)iS

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THE METALS gg

is preferred, the filtrate from Group II. after the addition of 3 g. of NHtCl

should be first rendered alkaline with (NHi)OH, heated to boiling and then
treated with an excess of colorless (NH4):S .

3. Vigorous stirring and heating of the precipitate will have the effect of
rendering it more compact and easier to filter.

4. If the filtrate has a dark brown or black color, Ni Is probably present.

5. The filtrate is at once acidified with acetic add to destroy the excess
of (NH,)25, which, on standing, would oxidize to sulphate and precipitate
the alkaline earths. Rendering the solution acid also prevents the formation
of (NHJjCOg from the absorption of atmospheric CO,. (tiH,)fiOf, if
formed, would also precipitate the alkaline earths.

6. The H^ is expelled because, like (NHJ^S, it is capable of being
oxidized partially to HgSO, on exposure to air.

7. The residue obtained may consist of NiS (when (NH,)gS has been
used as the precipitant) and coagulated S, and may be tested for Ni either
with a borax bead in the O. F., or by solution of the ppt. in hot dil. HNO^
rendering alkaline with NH,OH and adding dimethylglyoxime.

8. The precipitate is rapidly filtered with the aid of a fluted filter in
order to prevent the atmospheric oxidation of the sulphides to sulphates ; for
the same reason, it is recommended that the wash water contain, a little
(NHj)jS. NH^Cl is added to the wash water to prevent the precipitate
from passing through the filter in the colloidal condition. It is also well to
keep the funnel covered as much as possible during the filtering and washing
to minimize the oxidizing influence of the air.

9. The separation of Ni and Co from the remaining metals by the use of
HCl (i : 9) is not complete ; small amounts of Ni and Co may pass into solu-
tion, while portions of FeS and other add-soluble sulphides may be mechani-
cally inclosed by S and thus escape solution by the add.

10. A black residue does not prove the presence of Ni or Co for the rea-
son stated in note 9 ; it may be FeS indosed by S. It is also well to remetn*

' ber that metals of the Second Group, that have not been completely predpi-
tated by H^S, will appear at this point.

11. The experiments of Curtman and Rothberg show that in mixtures of
the sulphides of Ni and Co contdning as little as y^a CoS, a blue bead is
obtained. With 2.5^ of CoS uncertain results are obtained, while with ify
or less of CoS, the mixtures give brown beads. *

12. Evaporation to 1 or 2 drops will siifBce ; if the evaporation is carried
to the point of dryness, care must be taken not to ignite the residue. Should
die residue be acddentally ignited, redissolvA in hot aqua regia and evaporate
again to a few drops.

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lOO QUALITATIVE CHEMICAL ANALYSIS

13. These conditions must be closely adhered to. KNO, precipitates Co
best in a concentrated solution acid with acetic acid ; no mineral acid is per-
missible, owing 10 the solubility of the precipitate therein. The free HCl is
neutralized by the addition of NaOH in slight excess and the latter in turn is
neutralized by acetic acid. Should a larger volume than lo cc. be obtained
in making the test, it is recommended that the solution be evaporated to
lo cc. before saturating with KCl.

14. Under the conditions stated in Note 13, complete precipitation of Co
by KNO, takes place after a lapse of 24 hours. By saturating the solutioQ of
Co with KCl, in which K,Co(NO,)^ is insoluble, and by using an excess
of KNOj, the precipitation of Co may be rendered complete ia a half hour.

15. Not infrequently a precipitate of uncertain color is obtained with
NaOH. In that case the presence of Ni cannot be considered proved until a
characteristic Ni bead is obtained. It is however better to employ the di<
methylglyoxirae text which is more sensitive and characterisdc for Ni.

16. The solution is evaporated to I cc. to remove the excess of HQ
which, if present, would neutralize the NaOH next to be added. The HjS is
expelled at the same time.

17. Na^O, added to water even in the cold decomposes, giving NaOH + O.
At higher temperatures the decomposition takes place violendy. NaiO^
should, therefore, be added in small portions to the cold solution with con-
stant stirring ; the final mixture, which should be strongly alkaline, must
be boiled for a minute to decompose the excess of NajOj and the perchromates
which first form. The Na^Oj furnishes the oxygen necessary for the oxidation
of the chromite to chromate. It is important to remember that unless the
solution is strongly alkaline, some Zn will be precipitated on boiling and
diluting the mixture, due to the reversibility of the reaction, thus : —

Zn{OH)i + 2 NaOH^NajZnO, + 2 H^.

18. Any Ni and Co dissolved by the 1.02 HC will appear at tbb point;
their presence, however, does not interfere with the tests for Fe and Mn.

19. A decidedly blue firecipUate should be obtained if Fe is present. A
blue coloration or a brown or white precipitate is not to be taken as proof
of the presence of Fe. In making this test, car.e must be taken not lo add more
than a few drops of K,Fe(CN)g, as the precipitate is soluble in an excess.

20. If the filtrate is yellow, Cr is present ; if colorless, the test for Cr need
not be made. A portion of this solution may be tested directly for Cr by
acidifying with HNOj, cooling thoroughly, adding i cc. each of ether and 3^
HjOi and shaking. A blue color in the ether layer proves the presence of Cr.

21. The NH,a is added to prevent a partial precipitation of Zn.

22. An excess of NH^OH b to be avoided because of the slight solubility
ofAKOH), in excess.

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THE METALS lOi

23. The Co(NO,)i solution mnst be very dilute; if strong, it will, on
ignition, yield black CoO, which will obscure the blue color of cobalt Rumi-
nate. The same applies to the conflnnatory test for Zs.

24. It not infrequently bappiens that the solution contains sufficient sul-
phates to cause a precipitate of BaSOj (while) to form along with the BaCrO,
(light yellow), thus obscuring the test for Cr; hence the necessity of making
the confirmatory test.

25. The addition of NaCiHgO] represses the ionization of the acetic add
with the result that the solvent action of the latter on BaCrO. is reduced to a

26. If the filtrate from the BaCrO, is not clear, filter again, through another
double filter, and repeat this treatment until a perfectly clear 0trate is obtained.

27. If a black ppt., due to FeS, NiS, etc., is obtained, add dil. HCl, heat,
and filter. Render filtrate alkaJine with NaOH, add a little NaaOj, boil, dilute,
and filter. Test filtrate with HiS. A white ppt. is ZnS.

28. A slight precipitate of Al(OH)s is nearly always obt^ed, bdng de-
rived from the reagents as well as from the action of NaOH on the glass.
Judgment must therefore be exercised in reporting the presence of Al in the
substance analyzed.

GROUP IV. THE ALKALINE EARTHS
The alkaline earth metaJs, barium, strontium, ;.aicP,:cat(:^um, ,-'-, :
are distinguished from the metals of the precediftig grpup by the '"' "
fact that their salts are neither predpitated**tJ/'t^.-pt>r,J^," :',;
(NH4)aS; they are grouped together and are distinguished from
Group V. by reason of their common property of being precipi-
tated by (NHj)3C05 in the presence of NH4CI.

As the " analytical " grouping happens to be identical with
their classihcation according to the Periodic Law, the order-of
variation in properties becomes an easy matter to remember ; for,
in most cases, the solubilities of the compounds of strontium are
intermediate between those of barium and calcium. Unless the
acid radical imparts a color, the salts of the alkaline earths are
white or colorless, and, for the most part, insoluble in water.

The sulphides, like those of aluminum and chromium, can
only exist in the dry state ; when treated with water, they are at
once hydrolyzed with the formation of the hydroxide and the
evolution of HjS.

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I02 QUAUTATIVE CHEMICAL ANALYSIS

Reactions of the Salts of Barium
Many of the salts of barium are insoluble in water; excepting
the sulphate and fluosilicate, all are, however, soluble ia dilute
hydrochloric acid.

1. Ammonium Hydroxide (free from carbonate), when added
to a solution of barium salts, does not yield a precipitate. If,
however, the clear alkaline mixture is exposed to the air, or if
ammonium hydroxide from the reagent bottle * is used, a tur-
bidity results from the formation of barium carbonate. The
hydroxide is not precipitated because of its ready solubility in
water (i part in 20 of cold water): —

BaCL, + 2 NHjOH =■ Ba(OH)j + 2 NH^Cl;

Ba(OH), + COa = I BaCOj + H3O ;

2 NH^OH + COj = (NH,)aCOj + HjO;

(NH4),C08 + BaCla = | BaCOg +-2 NH^CL

2. Ammoalam Sulphide (free from carbonate) does not pre-
cipitate barium salts; on standing in the air, or with (NHj)3S
from thejteagpnt bottle, a slight turbidity results from the forma-

.."tioo of lAriiini carbonate. Reagent (NH^)jS, being an alkaline
V iguidj:*iit m cdhsequence of absorption of atmospheric COj,
; ^-ofltiiirtV little" (KHi)aC03, hence it will yield an immediate tur-
bidity with barium salts : —

(i) (NH^)jS + BaCl3= BaS + 2 NH^Cl;

(2) BaS + 2 HjO = Ba(0H)3 + f HgS ;

(3) Ba(OH)a + COa=:^BaCOB+HaO.

3. Ammonium or Sodium Carbonate produces in neutral or
alkaline solutions of barium salts a white amorphous precipitate
of BaCOg, which, on standing or heating, becomes crystalline: — ■

BaCIj + (NH4)aC08 = | BaCOg + 2 NH^Cl.

* All alkaliae liquids will, on exposore to' the air, absorb COg, intb th« fbn>i«tioa
of carbonate proportional to the amoant of CO] alnocbed; the reagent ammonium
hydroxide will, therefore, always contain a little {NH,)>COi, and hence will yield a
d^ht precipitate with the salts of the alkaline eaiths (see equations).

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TEE METALS 103

The precipitate is slightly soluble in NH4CI; therefore, in very
dilute solutions of barium salts containing much NH4CI, ammo-
nium carbonate does not produce a precipitate. The precipi-
tate is easily soluble in acids, even in acetic and carbonic
acids : —

BaCOg + 2 HCaHgOj = BsLiC^HsO^^ + HjO + f COj;
BaCOg + HjCOg = BaH/COgV
Boiling the dicarbonate decomposes it with the evolution of
COa and precipitation of the normal carbonate : —

BaHj(COB)j + (heat) = | BaCOg + HjO + f CO*.

4. Dilate Solphaiic Add or any soluble sulphate produces even
in very dilute solutions of barium salts a heavy, white, finely
divided precipitate of BaSO^, practically insoluble in water (i
part in 400,000 parts of water) : —

BaCIj + HjSOj == I BaSOj + 2 HCl.
The precipitate is insoluble in alkalies, and is nearly insoluble
in dilute but is somewhat soluble in strong acids. Boiled with
a strong solution of Na,COg, it undergoes partial decomposition,
according to the equation : —

BaSOi + NaaCOj^tl BaCOg + NagSO,.

The decomposition is incomplete because of the reversibility
of the reaction. If, however, the niixture is filtered, and the
residue of BaCOg and unchanged sulphate is boiled with a fresh
NajCOg solution, more BaSOj will be converted to carbonate.
By repeating this process a sufficient number of times, one can
transform all the sulphate to carbonate. As the carbonate, after
thorough washing, is easily soluble in acids, it will be seen that
this procedure offers a means of getting an insoluble sulphate
into solution.

A better and more etpeditious method of rendering the re-
action complete consists in fusing the sulphate of barium with
several times its weight of NajCOg. Under these conditions,
the reaction proceeds to completion in one operation. On
cooling the melt, boiling it with water, and filtering, there will

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I04 QUAUTATIVE CHEMICAL ANALYSIS

rem^ on the filter a residue of BaCOg equivalent in amount to
the BaSOf taken ; the carbonate is then taken into solution
with dilute hydrochloric acid. The method of fusion with
alkali carbonate just outlined is of general application and is
employed where it is-desired to take into solution substances
which are insoluble in water and in acids. The sulphates of
strontium and calcium, though not as insoluble as that of
barium, are sufficiently insoluble to be classed with insoluble
substances and may be got into solution by the fusion method.
PbSOi, SrSOj, and CaSOj may be completely converted into
carbonate by the first method.

5. Potassltim Chromate precipitates from neutral or acetic
acid solutions yellow barium chromate : —

KjCrOi + BaCla = \ BaCrO, + 2 KCL

The precipitate is practically insoluble in water (i part in
250,000) and in acetic acid (distinction from Sr and Ca),
but is soluble in mineral acids. With potassium dichromate
(KjCrgO^) only partial precipitation results : —

2 BaCIa + KjCraO, + HaO = 1 2 BaCrO, + 2 KCl + 2 HCl.

This is due to the formation of HCl, which exerts a solvent
action on BaCrOj; the addition of sodium acetate will render
the precipitation complete.

BaCrOj, like BaSO^, is best precipitated in a boiling solution ;
for under these conditions the precipitate is obtained in a form
which can be readily filtered and washed, without passing
through the pores of the filter.

6. Ammonitim Oxalate precipitates from moderately dilute
solutions white barium oxalate, somewhat soluble in water
(i part in 2600) and completely soluble in boiling acetic acid
(distinction from Ca) : —

BaCIa + (NH4)aC304= | BaCaO, + 2 NH^CI.

7. Disodlnm Phosphate precipitates in neutral solutions white
flocculent BaHP04 ; in ammdniacal solutions, sodium phos-

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TSE METALS loj

pbate throws down the tertiary phosphate. The precipitates
are easily soluble in dilute acids, even in acetic acid : —

NajHPOj + BaClj = 2 NaCl+ \ BaHPO,;
2 NajHPO^+3 BaCla+2 NH8=|Baj(P04)2+4 NaCH-2 NHjCL
8. Fiame Reaction. Barium salts, preferably the chloride,
when heated on a platinum wire in the bunsen Same, impart
to it an apple-green color ; frequently it is yellowish green, due
to sodium as an impurity. The reaction becomes more delicate
if the wire is first moistened with concentrated HCL

Strontium
I. Ammoniain Hydroxide. Same as with Ba salts.
a. Ammonium Sulphide. Same as with Ba salts.

3. Ammonium Carbonate precipitates white SrCOg, more in-
soluble in water than BaCOg; in other respects, it possesses
about the same solubilities as BaCOg.

4. Dilate sulpharic add or any soluble sulphate yields a white
precipitate of SrSO^. The precipitate is more soluble in water
(i part in 7000) and in acids than BaSO^, aad, as a consequence,
is precipitated from very dilute solutions only after some time ;
it is, however, much less soluble in water than CaSO^, the latter
dissolving in water to the extent of i part in 500. -.

SrSOj is practically insoluble in a strong solution of (NH4)2SOt,
even on boiling (distinction and method of separation from Ca).

5. Saturated CaSO^ Solution yields with dilute solutions of
strontium salts a precipitate of SrSO^, which forms only after
some time (distinction from Ba, which yields an immediate pre-
cipitate). Precipitation in this case, as well as in 4, is promoted
by heating, and is retarded by the addition of acids. From
concentrated solutions of Sr salts, an immediate precipitate is
obtained.

6. Potassium Chromate does not yield a precipitate with dilute
solutions of strontium salts or with concentrated solutions add
with acetic acid (distinction from and method of separation from

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lo6 QVAUTATIVE CHEMICAL ANALYSIS

Ba). From neutral concentrated solutions, however, a yellow
crystalline precipitate of SrCrO^ forms which is soluble in acetic
acid.

7. Ammonlnm Oxalate. Same as with Ba. SrCgO^ is only
sparingly soluble in acetic acid.

8. Disodlum Phosphate. Same as with Ba.

9. Flame Reaction. Strontium salts, preferably the chloride,
when heated on a platinum wire in the bunsen flame, impart to
it a deep red color.

Calcium

1. Ammonlnin Hydroxide. Same as with Ba.

2. Ammonium Sulphide. Same as with Ba.

3. Ammonium Carbonate precipitates white amorphous CaCOg,
becoming crystaUine on heating ; it is more insoluble in water
than BaCOg, but in other respects its solubilities are about the
same as those for BaCOg.

4. Dilate Salpburlc Acid or any alkali sulphate does not pro-
duce a precipitate from dilute solutions. From concentrated
solutions a white precipitate of CaSO^ is obtained which is
appreciably soluble in a hot concentrated solution of (NH^^SO^
(distinction and method of separation from Sr). A saturated
solution of CaSO^, of course, does not precipitate Ca salts (dis-
tinction from Sr and Ba).

5. Potassiom Chromate does not yield a precipitate from
dilute neutral solutions or from concentrated solutions acid with
acetic acid.

6. Ammonium Oxalate produces a white crystalline precipi-
tate of calcium oxalate immediately from strong solutions and
slowly from dilute solutions of calcium salts. The presence of
free ammonia, or heating, facilitates the precipitation. The pre-
cipitate is practically insoluble in water (i part in 170,000) and
in acetic acid, but is readily soluble in mineral acids ; —

CaC,04 + 2 HQ = CaClj + HjCaO,.
This is a most delicate test for Ca.

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TBE METALS 107

7. Dlsodltun Phosphate gives the same reactioa as with Ba.

8. Flame Test Calcium salts, preferably the chloride, when
heated on a platinum wire in the hunsen flame, impart to it a
yellowish red color.

Outline of the Method of Analysis for Group IV

With certain mixtures it is possible, with a Uttle practice, to
detect all the metals of this group when occurring together by
the simple flame reactions, as the characteristic colors do not
all appear at the same time ; the latter fact is due to the differ-
ence in the volatility of the chlorides. By an analysis of the
flame colorations with the spectroscope it is not difficult to de-
tect all the alkaline earths, even when they are all present to-
gether in the same solution. But as the spectroscopic and
flame tests do not distinguish between significant amounts and
mere traces due to accidental impurity, they cannot be relied
on to determine the composition of an unknown substance.
They are, however, exceedingly valuable as confirmatory tests
and for the detection of traces. If the filtrate from Group III.,
concentrated to a few cc, fails to yield a flame coloration, the
absence of Group IV. would be proved, although the reverse
would not hold.

If the solution to be analyzed for Group IV. is the filtrate
from Group III., it will contain a sufficient amount of NH^Cl
to prevent the precipitation of Mg along with the alkaline
earth carbonates on adding the group reagent, (NH^jjCOs-
The precipitated carbonates are dissolved in acetic acid and
from this diluted solution the barium is separated from the re-
maining metals of this group by precipitation with KjCrO^.
After filtering the BaCrO^, the filtrate will contain, besides Sr
and Ca, an excess of KaCfjOj. By reprecipitating the Sr and
Ca as carbonates, and filtering, they can be separated from the
excess of chroraate. If the carbonates are now dissolved in
acetic acid, and the resuhing solution is boiled with a solution
of {NH^jjSOj and filtered, the Sr will be on the filter as
SrSOj, while the Ca will pass into the filtrate. From the

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io8 QUAUTATIVE CHEMICAL ANALYSIS

latter the calcium may be precipitated as CaC^O^ witli
(NH4),Cb04.

The separation of Sr and Ca by the use of a boiling solution
of (NHj)jS04 is not complete; some CaSO^ remains undis-
solved, while at the same time a small amount of SrS04 goes
into solution. The necessity for making confiTTnatory flame
tests is therefore apparent.

The filtrate from Group III., which has been addified with acetic acid,

boiled, and filtered from the coagulated sulphur and NiS, as described under
Scheme III., should be perfectly clear; if cloudy, it should be boiled again for
a few minutes and repeatedly filtered through a double filter until a perfectly
dear liquid is obtained ; it should then be concentrated by evapiMstion to
about 30 cc*

Preliminary Test for Group IV. To a small portioa of the clear filtTa.te in a
test tube add NH^OH to alkaline reaction and then a slight excess of
(NH,)jCOg, and warm; a white ppt. proves the presence of Group IV. If no
ppt. is obtained, the absence of more than traces (i) of the alkaline earths is
indicated ; in that case proceed to Scheme V.

If the preliminary test shows the presence of Group IV., the entire filtrate
contained iu a beaker is made alkaline with NH^OH and is heated nearly to
boiling ; (N H,)jCO, is then added in slight excess and the mixture b wanned
(but not boiled) (2). The ppt. is allowed to settle and then filtered. The
filtrate (3) should be received in a small beaker labelled Group V,, covered,
and reserved. The ppt. may consist of BaCOj, StCOj, and .CaCOj. Wash
once with hot water and reject the washings. Dissolve the ppt. on the filter
with the least amount of hot dilute acetic acid (4). Make the volume up to
40-50 cc. by dilution with water (;), heat to boiling, and, while boiling, add
KjCrO, drop by drop till precipitation is complete. Allow the ppt. to settle
and filter (using a double filter) by decantation. Finally, with the aid of hot
water, bring the ppt. on the filter.

* Any NHiG which separates out during the evapotation should be filtered ofT and
rejected. The removal of an uimecessiiTily large excess of ammonium salts at thii
point is a decided advantage, because it ledaces the amount of material that must be
temoved by volatilization in the tubsequcnl examination for Group V.

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THE METALS

X09

Kcsidne is yd- Filtrate (6) m^y contain Sr and Ca as acetates and

low BaCrO,. K,Cr,OT. To remove the latter, add NH^OH to alkaline

Wash twice with reaction and then (NH J,CO, till precipitation is complete ;
;r and re- heat and filter. If no ppt. forms, the absence of more than
washings, traces of Sr and Ca is indioted. Residue is SrCO, and
Confirm by dip- CaCOg. Reject filtrate. Wash ppt. with hot water until
ping dean Ft the washings are no longer yellow ; reject washings. Db-
(9) mois' solve ppt. on filter in the least amount of hot dil. acetic
tened with cone, acid, and dilute the resulting solution with an equal volume
HCl into ppt., of water.

andholdinflame. Prellminaiy Test for Sr (7), 'Pom Avery smail portion

Do this repeat- of this solution into a test tube and add a little CaSO, so-
edly ; a green lution, heat to boiling, and allow to stand for a few min-
coloratioD ap- utes. (a) A slowly forming ppt. or doudiness indicates
pearing after the presence of Sr; proceed according to (a), (b) No
time con- ppt. or cloudiness proves the absence of Sr; proceed ac-
firms the pres- cording to (S). ,■'

ence of Ba (10), (u) If Sr is present, rendpr' the remainder of the solu-

tion alkaline with NH,OH, add 5 cc. of (NHj)^0„ boU
for a few minutes, and filler. Ppt. is SrSO,. Wash with
hot water and confirm by flame test (8). Test filtrate
for Ca by adding (NH()jCiOj. A white ppt. insol. in
HCjHjOj is CaCjOj. Confirm by flame test.

(*) Make solution alkaline with NH^OH and add
(NH,):CaOj. A white ppt. insol. iuacedcaddis CaC,0,.
Confirm by flame test.

sarsa

1. Teats for trace* of alkaline earths. If no predpitate is obtained with
(NHf)^0„ treat a small portion of the solution with dilute H^O^, boil, and
allow to stand for some time- A white predpitate o^BaSO^roves the pres-
ence of Ba, Treat another small porti^^^^^|^|HHB8^kaline, add
('NH4)2C,0,, heat to boiling, and allonM^^I^^*Cro^iness or white pre-
dpitate proves the presence of Ca. Traces of Sr are best tested for by
means of the spectroscope,

2. The mixture must not be boiled, because at the boiling temperature
(NH^jCOj is decomposed according to the equation —

(NH,),COa = 1 2 NH, -h H,0 -H 1. CO,.

The carbonates, which are first thrown down as an amorphous predpitate, are
converted by heating and stirring into the crystalline form which can be
readily filtered and washed.

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no QVAUTATIVE CREMICAL ANALYSIS

3. To insure completeness of predpitatjon, add a little (NHJ^CO, to the
filtrate ; if a precipitate foims, add it to the first ; if no precipitate forms, pre-
cipitation was complete. •

4. This is accomplished by pladng a test tube under the stem of the fiin-
nel and pouring on the precipitate a hot mixture of 5-10 cc of dilute
acetic add and an equal volume of water, allowing the add to pass through
the filter and pouri:^ the same add repeatedly through the filter till all the
predpitate is dissolved.

5. A preliminary test with K,CrOj should be made on a smail portion of
this solution. If a predpitate is obtained, Ba is present and the entire solu-
tion should be treated with KgCrO^ as described in the scheme. If no precipi-
tate is obtained, Ba is absent: In that case the solution should not be treated
with KjCiO^ solution, but on a small porlion make a preliminary test for Sr
with CaSO, solution ; if present, treat the remainder of the solution accord-
ing to (ii) ; if absent, proceed to (b) .

6. BaCrOp even when predpitated in a boiling solution, may pass through
the filter, yidding a doudy filtrate \ when this is the case, the filtrate must be
boiled again and reliltered.

7. It is important to use only a portion of the liquid for the prdiminary
test. If by mistake the entire filtrate is used, the test for Ca obviously cannot
be made.

8. The confirmatory test for Sr b made by moistening the predpitate with
concentrated HCl, dipping the wire into it and holding in the flame. A deep
red coloration confirms the presence of Sr. If all the Ba had not been com-
pletely predpitated as chromate, it will appear here as white BaSO^ but can
readily be distinguished from SrSOj by its failure to yield a red coloration to
the flame.

9. A ptffectly dean platinum wire must impart no color to the colorless
bunsen flame. When this is not the case, an impurity is indicated, and this
may be removed by one of the followicg methods :

(a) Any large partides of matter adhering to the wire must first be me-
chanically removed. The wire is then dipped into concentrated C.P. HCl,
contained in a weighing or small specimen tube, and then held in the flame
for several seconds. The acid dissolves and thus removes some of the ad-
hering material and partly converts some of the still remaining impurity on
the wire into chlorides which are volatilized in the flame. Repeat this opera-
tion several times ; finally dip wire into JresA add, and hold in fiame- It
dean, it should give no color to the flame.

Under no circumstances must tke wire, eUan or otherwise, he dipped into
the reagent bottle of acid. The efiidency of this method will be indicated by
the fact that the flame coloration becomes noticeably fainter with each treat-

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THE METALS III

(6) Shoold the above treatment, however, fail to cleanse the wire, it must
be dipped while red hot into borax, and heated until a bead fonns. By prop-
eriy manipulating the wire in the flame, the bead can be made to travel bade
and forth several times over the entire length of the wire. It is then shaken
<M. Should any solid material then adhere to the wire, it can now be readily
removed by scouring with sand. The wire is then treated with concentrated
HO as described in (a).

10. The Ft wire need only be dipped once into the BaCrO, precipitate.
After the first beating with HQ, it should be moistened with HCl again and
heated. This is to be repeated several times without redipping into the
BaCrO, precipitate.

GROUP V

Group V. embraces the metal magnesium, the alkali metals
potassium and sodium, and the metallic radical ammonium
{NH^). Magnesium is closely allied from an analytical stand-
point to the alkaline earths, iot its hydroxide, carbonate, and phos-
phate are insoluble in water. It has been placed in Group V.
for the reason that in the course of complete analysis it will be
found in the last filtrate along witii the alkali metals. This, of
'ourse, is due to the presence of NH^Cl in precipitating the
third and fourth groups.

The test for NH^ is not made on the final filtrate, because
the latter will always contain ammonium salts added in the form
of reagents in the regular course of analysis. The test, there-
fore, must always be made on a portion of the original
substance. The other alkali metals, lithium, caesium, and
rubidium, belong to this group, but have not been included
because of their rare occurrence.

Omitting consideration of magnesium, which serves as a
bridge between groups IV. and V., it may be stated that the
chief characteristic of the alkali metals is the fact that nearly all
their salts are soluble in water; thus, the chloride, sulphate,
sulphide, nitrate, phosphate, oxalate, carbonate, and hydroxide
are soluble in water ; indeed, their aqueous solutions have been
used as reagents. Excluding NH^, all the alkali metals give
characteristic flame and spectroscopic reactions.

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Iia qUAUTATIVE CHEMICAL ANALYSIS

Magnesium

Magnesium salts are colorless. With the exception of the
hydroxide, carbonate, phosphate, arsenate, and arsenite, all the
salts of magnesium are soluble in vater. They do not color
the bunsen flame. Neither NH^OH, (NH4)3S, nor (NH^)3C0a
precipitates magnesium salts in the presence of a sufficient
amount of ammonium chloride, hence the classification of mag-
nesium with the alkali metals.

1. Ammonium Hydroxide gives a partial precipitation of gelati-
nous magnesium hydroxide, Mg(OH)g, readily soluble in am-
monium salts : —

MgSO, + 2 NHjOH 5t| Mg(OH)j + (NH4),SO^.

The precipitation is only partial in consequence of the forma-
tion of an ammonium salt as a by-product of the reaction. The
precipitate is readily soluble in acids. The solubility of the
precipitate in NH^ salts, or, what amounts to the same thing,
the non-precipitation of Mg salts by NH^OH in the presence of
a sufficient amount of NH^ salts, is a phenomenon of the same
order as that already met with in the cases of ferrous, man-
ganese, and zinc compounds.

2. Sodium, Potassium, or Calcium Hydrozide completely pre-
cipitates, in the absence of NH^ salts, Mg(OH)j, insoluble in
excess and nearly insoluble in water, the solubility being i part
in 10,000. The washed precipitate is soluble in NH4 salts : —

MgSO^ + 2 NaOH =| Mg(OH), -|- NajSO^.

Boiling promotes precipitation.

3. Ammonium Carbonate, in the presence of NH^ salts, gives-
no precipitate. In solutions containing no NH^ salts, a white
basic salt precipitates on standing or on boiling. The composi-
tion of the precipitate is variable, depending upon the condi-
tions of concentration and temperature : —

4 MgSOi -I- 4 (NH^>,COg + HjO =

I Mg,(COsUOH)a -I- 1 CO a + 4 (NH,)3S04

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THE METALS 113

4. Disodlom Phosphate, when added to a neutral solution of a
Mg salt, precipitates fiocculent MgHPO^: —

NaaHPO, + MgSOj = | MgHPO^ + NajSO,.

If, however, NH^Cl and ammonia are added to the solution
of a Mg salt before adding the sodium phosphate, a character-
istic white crystalline precipitate of ammonium magnesium
phosphate forms : —

MgClj + NaaHPOi + NH8=4.NH,MgP04 + 2 NaCI.

From dilute solutions the precipitate forma slowly, but it may
be hastened by cooling and vigorously stirring the mixture.
The precipitate is slightly soluble in water (i part in 13,500 at
23° C), but is practically insoluble in 2.5 per cent, ammonia
water. It is readily soluble in acetic acid. The addition of
NHjCl prevents the formation of the hydroxide when ammo-
nium hydroxide is added. This is a most delicate test for Mg.

5. AmmoDlam Oxalate gives with dilute solutions of magne-
sium salts no precipitate ; from concentrated solutions, however,
it yields a white precipitate of MgCjOj. The presence of NH^
salts renders the precipitation incomplete.

6. HgS, (NH4)3S, and HaSO^ do not precipitate magnesium
salts.

Potassium

With the exception of the acid tartrate, cobaltic nitrite, chlor-
platinate, and perchlorate, nearly all the salts of potassium are
soluble.

I. HydrochlorplatiaiG Acid (H^PtCIg) produces in neutral or in
concentrated acid solutions of potassium salts a yellow crystal-
line precipitate of potassium chlorplatinate (KaPtClj) : —

2 KCl -t- HjPtCla =|KaPtCle + 2 HCl.

From moderately dilute solutions the precipitate separates out
only after standing, but may be hastened by cooling, stirring,
or shaking the mixture vigorously in a test tube. This applies
to nearly all crystalUne precipitates. The precipitate is soluble in

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114 qUAUTATlYE CBEMICAL ANALYSIS

alkalies ; it dissolves in water to the extent of i part in ic» at
1$" C. It is practically insoluble in 80 per cent, alcohol. On
ignition it decomposes according to the following equation : —
KjPtClg = 2 KCI+|Pt +f 2Cla.
Solutions of potassium iodide and potassium cyanide do not
give this precipitate ; they should first be changed to chloride by
evaporation with concentrated HCL As NH^ salts yield a simi-
lar precipitate they must be removed before tiie test is applied.

2. Tartaiic'Acid (HgC^H^Og) produces in neutral solutions of
potassium salts, which are moderately concentrated, a white
crystalline precipitate of potassium acid tartrate : —

KCl + HjC^H^Ofl =|KHC4H40e + HCl.
Precipitation may be hastened by vigorously shaking the mix-
ture. The precipitate is soluble in alkalies and in mineral acids.
A solution of sodium acid tartrate (NaHC^H^Og) is preferable,
as it does not yield any free acid as a by-product : —
KCl-f NaHC^Hp, =|KHC4H40, + NaCl.

The solubility of the precipitate in water at 15" C. is i part in
222. The reaction is a little more than twice as sensitive as i.
Ammonium salts must be absent as they yield a similar pre-
cipitate with the reagent.

3. Sodium Cobaltic Nitrite [NaaCo(NOa)B] yields, with solu-
tions of potassium salts acidified with acetic acid, a yellow pre-
cipitate of potassium cobaltic nitrite [K3Co(NOj)g] . From dilute
solutions the precipitation may be hastened by warming the
mixture. The precipitate is soluble in water to the extent of i
part in 11,000 at 15° C. and is therefore the most sensitive of
the reactions mentioned. The test cannot be applied in the
presence of NH^ salts for the reason that the latter yield a sim-
ilar precipitate.

4. Flame Reaction. Potassium salts, preferably the chloride
and nitrate, when heated on a platinum wire in the bunsen
flame, impart to it a violet color. The sensitiveness of this reac-
tion was given by Bunsen to be 0.001 mg. KCl. The presence

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THE UETALS 115

of even small amounts of sodium compounds interferes with this
reaction by masking the color. If, however, the flame is viewed
through several thicknesses of cobalt glass, the latter will absorb
the yellow rays and thus permit the violet color to be seen.

5. When heated just below a red beat, potassium chloride is
not volatilized (distinction from NH| salts).

Ammonium
The ammonium salts very closely resemble the potassium
compounds. They have the same crystalline form and, in gen-
eral, about the same solubiUty.

1. HydrocMorplatlnic Add (HjPtCIg) precipitates, under the
same conditions given for potassium compounds (which see),
a yellow crystalUne precipitate of ammonium chlorplatinate,
(NH,),PtCle:~

2 NH^Cl + HaRCi, ^^NH^^jPtCla + 2 HCL

The precipitate may easily be distinguished from the correspond-
ing potassium compound by the fact that it is decomposed by
an excess of NaOH with the evolution of NHg : —

(NH4)jPtCle + 2 NaOH = NajPtCl, + f 2 NHg + 2 H,0.

When strongly heated, it leaves a residue of platinum sponge
only (distinction from the K compound). Ammonium chlorplati-
nate is somewhat less soluble in water than the corresponding
K compound ; it is insoluble in alcohol.

2. Sodium Cobaltlc Nitrite yields with solutions of ammonium
salts a yellow precipitate similar to that given by potassium salts.
Hence before testing for potassium with this reagent, all the
ammonium salts must be removed.

3. Tartaric Add (HaC^H^Og) or NaHC^H^Og gives from con-
centrated solutions of ammonium salts a crystalline precipitate
of NH^HCjHjOj. The precipitate is soluble in acids and in
alkalies, and is very much more soluble in water than the cor-
responding K compound ; for this reason it is not a good test.

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Ii6 QUALITATIVE CHEMICAL ANALYSIS

It may be distinguished from the coTrespooding K compound
by the evolution of NHg when treated with an excess of NaOH.

4. Sodium Hydroxide. All ammonium compounds, when
heated with an excess of caustic soda, potash, or lime, undergo
decomposition with the evolution of ammonia gas; the latter
may be detected by its characteristic odor or by the ability of
the gas evolved to turn moistened red litmus paper blue : —

NH4CI + NaOH = f NHg + NaCl + H3O ;
2 NH4CI + Ca(OH), =: \ 2 NHg + CaCl, + 2 HjO.

The evolved NHg may be further recognized by holding in
the escaping vapor a piece of filter paper moistened with mer-
curous nitrate solution. Ammonia, if present, will blacken the
paper in accordance with the following reaction : —

2 HgNOg + 2 NHg = |(NH,HgNOB + Hg) + NH,NO,.

5. For the detection of minute amounts of ammonia, such,
for instance, as are present in drinking water, an alkaline solu-
tion of mercuric potassium iodide, known as Nessler's reagent,
is used. With this solution, a yellow coloration is obtained
which deepens in color, becoming brown with relatively greater
amounts. With still greater amounts a brown precipitate is
obtained.

2{2KI.HgI,) + NH8+3KOH = |NHgjI-HjO + 7KI + 3HaO.

6. All ammonium salts are volatilized at a temperature just
below a red heat (distinction and method of separation from
Na and K salts), some undergoing decomposition at the same
time.

SODHJU

All of the salts of sodium, with the exception of the pyroanti-
monate, are soluble in water.

I. Potassium PTnantlmonate Solution (KtHsSbjO^) precipi-
tates from neutral or slightly alkaline solutions of sodium salts
that are fairly concentrated, a white crystalline precipitate of
sodium pyroantimonate (NaaHaSbaO,). Precipitation may be

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TEE METALS 117

hastened by shaking the mixture vigorously in a test tube.
Sodium pyroantimonate is soluble in boiling water to the extent
of I part in 300 : —

KaHjSbjOj + 2 NaCl = 4 Na3HjSbj07+ 2 KCI.

The solution must not be acid, for then decomposition of the
reagent results with the precipitation of amorphous pyroanti-
monic acid : —

KaHjSbaOT + 2 HCl = | H,SbjOT + 2 KCI.

All other metals, with the exception of K and NH^, must be
removed, for they too yield precipitates with the reagent

2. HydrochloTplatJiiic Add, and Tartaric Acid, do not precipi-
tate sodium salts.

3. Sodltim Cobaldc Nitrite does not give a precipitate with
sodium salts (distinction from K and NH^).

4. Heated just below a red heat, sodium compounds are not
volatilized (distinction from NH,).

5. Flame Reaction. — Sodium compounds color the bunsen
flame yellow even when the quantity is very small. Bunsen
and Kirchhoff state that as small an amount as flftoiaflo of a
milligram of sodium will give a flame test. To distinguish
between a trace and a significant amount, attention must be
given to the intensity and duration of the coloration.

Outline of the Method of Anal;^ for Group V
As the special tests for most of the metals of Group V. are
not interfered with by the presence of the others, it is needless
in most cases to effect their separation before applying the test ;
thus, the precipitation test for potassium may be made in the
presence of sodium, and the test for Mg may be made in the
presence of all the alkali metals, for the latter are not precipitated
by Na^HPOj. The test for Mg is therefore carried out on a
small portion of about one-third of the filtrate from Group IV.
It must, however, be remembered that NaaHPO, precipitates
the alkaline earth metals; and as the latter are usually present

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Ii8 QVAUTATIVB CHEMICAL ANALYSIS

in small amounts in the last filtrate by reason of the sl^;ht solu-
bility of their carbonates in NH4Q, they must first be removed
before the test can be applied. This is ax:compIished by adding
a little (NH4)jS04 and (NH4)jCj04, boiling, and filtering off
the precipitated alkaline earths in the form of sulphates and
oxalates. The filtrate, after concentration, may then be tested
for magnesium.

The remaining two-thirds of the original filtrate is used for
the detection of Na and K. As this filtrate contains a large
amount of ammonium salts accumulated in the course of the
analysis, and as the latter interfere with the precipitation tests
for K by yielding similar precipitates, it is necessary to remove
them before the test for K is made. This is accomplished by
taking advantage of the fact that at a temperature just below a
red heat, all NH4 salts are volatihzed. The NH4 salts removed,
the residue is moistened with a little water, and the dame tests
are applied. If an intense yellow coloration is obtained which
persists for some time, the presence of Na is proved ; the flame
may then be further examined for potassium by viewing it
through several thicknesses of cobalt glass. If a violet-colored
flame is obtained in the first place, Na is absent. In either case,
a confirmatory test for potassium should be made by any one of
the precipitation tests.

Ammonium is not tested for in this group for the previously
mentioned reason that NH4 compounds in the form of reagents
have been added to the solutdon in the course of the analysis.
The test, which consists in Uberating NH, by heating with an
excess of NaOH, must, therefore, always be made on a separate
portion of the ordinal substance.

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THE METALS

SCHBHB T

Asalyalf of the Filbate from &Dnp IV
This will contain, besides Mg and the alkalies, traces of the
alkaline earths which were dissolved by NH^Cl. Divide into
two unequal portions.

In J test for Mg. Add a few drops of (NHJ^O, and (NH^jCjO^, boU
and filter. Reject any ppt. which may form (i). Concentrate the filtrate bj
evap. to 5 cc. (should any ammonium salts crystallize out, filter and reject).'
To filtrate contained in a test tube add NH4OH to alkaline reaction and then
add Na^HPO,. Shake vigorously and allow to stand several minutes. A
white ctyst. ppt. which b soluble in acetic add is NHjMgPOj.

In \ teat for Na and K. Evap. in a targe evap. dish, if the vol. of the
solution is large, to about i; cc- Transfer to a small dish and continue to
ev^. over a wire gauze until sputtering occurs ; then cover dish with a watch
glass and gently heat until the mass is perfectly dry. By means of a glass
rod, transfer to dish particles of salt adhering to the watch glass, place
uncovered dish on a pipestem triangle, and ignite (under hood) until no
more iiimes of NH^CI are given off, being careful to keep the dbh belme a red
heat and to heat the sides and rim as well as the bottom of the dish. With
the iud of a glass rod scrape any salt adhering to the sides of the dish into the
center, and stir up salt at the bottom as much as possible ; ignite again until
no more NH,0 (a) is given off. Cool. Transfer a small portion of the
residue to a watch glass, moisten with a drop of HQ, dip dean Pt wire into
it, and hold in flanie. A violet coloration proves the presence of K and
absence of Na. An intense yellow coloration (3) which persists for some
time proves the presence of Na ; in that case, examine flame for K either
with several thicknesses of cobalt glass or better with a spectroscope (4).

Teat for K. The remainder of the residue in the dish is dissolved in the
least amt of hot water (3 cc.) just addified with acetic add, and is filtered
through a small filter. To filtrate in a test tube add i cc of NajCo(NO,)^
warm, ahd allow to stand for several minutes. A yellow ppL confirms the
presence of K.

Test for HH,. This test is always made on a small portion of the ordinal
substance and never on the filtrate &om Groups III. and IV. To about
S cc. of the (Vj^wo/ solution or 0.3 — 0.5 g. of the original solid substance
contained in a small beaker, add NaOH till the resulting mixture, aAei
thorough stirring, is deddedly alkaline. Heat with stirring (5). Ammonia,
if present, will be made evident by its characteristic odor and by Its ability to
turn bhie a piece of red litmus paper held above the beaker.

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I20 QUALITATIVE CBEMICAL ANALYSIS

VOTES OB SCHEME V

1. Na^PO, precipitates all the metals except the alkalies and As, so that
the test for Mg can only be made in the absence of these metals. A floccn-
lent precipitate of AIPO4 sometimes aepaiates on adding Na^PO^ but the
latter is easily distinguished from NH^MgPO^ by reason of its insolubility in
acetic add. In concentrating the soludon to j cc., Al(OH)) may separate
out ; in that case, it should be filtered off before adding the Na^PO,.

Should a precipitate of doubtful form be obt;uned with Na^PO, and it is
desired to confirm the presence of Mg, the precipitate on the filter should be
treated with a little acetic add, the resulting dear filtrate made alkaline with
NH,OH, vigorously shaken, and allowed to stand for several minutes. If
Mg b present, a white crystalline precipitate will form.

It is not customary to remove the Mg before testing for the alkalies.
Should it be desired, however, to estimate the amount of K and Na, the Mg
may be removed by first expelling NH4 salts by evaporation of the solution to
dryness and thoroughly igniting the residue. The latter is then dissolved in
water and the Mg is predpitated with Ba(OH), solution, filtered, and the Ba
in the filtrate removed by predpitation with sulphuric acid, or with NH4OH
and (NHJjCO,.

2. Unless the last traces of NH^ salts are reop^wl, the predpitation test
for K will b^j^^less for t'he reason that NtCwi^^yield a similar predpi-
tate. During'fl^ygnition, the bottom of t^c^fetf must not be allowed to
reach a red G^ffise there will be dafl^-'of volatilizing NaCl and KCl. A
small amount of slack carbonaceous matter (dueito carbonization of small
quantities of pyfJRline which is usually present in the NH,OH) is left behind
along with the vhlorides of K and Na. This is, however, removed later
when the residue is treated with water and filtered before making the pre- '
dpitation test for K.

3. A fleeting ydlow coloration is not to be taken as evidence of the pres-
ence of Na. The coloration should persist for at least 6 seconds.

4. The test for K should be confirmed always by a predpitation test.

5. Stirring the mixture while heating is important because of the tendency
of the mixture to bump and the consequent danger of having the strongly
alkaGne mixture spurted into the eyes. Care should be taken in heating and
stirring to prevent any.of the alkaline liquid from coming in-contact with the
litmus paper. Failure to observe this precaution will vitiate the test.

If the ori^nal material is a solid instead of a solution, it is not necessary
to get it into solution in order to test for NH,. To a portion of the solid
substance in a beaker, add NaOH in slight excess, forming a paste, and heat
gently with stirring. The odor of NH, eVojjjpd . will prove the presence of

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THE METALS

ANALYSIS OF UNKNOWN SOLUTIONS FOR ALL GROUPS
To 25 cc. of station add HCI a^d filter.

AgCl,Pba»
HgO.

Analyze ac-
cording to
Scheme I.

Filtrate contains Groups IL-V. Bring to proper coaditioni
of acidity and pass in HtS. Filter.

Kealdne:
HgS, PbS,
Bi,S„ CuS,
CdS, As,S^
SbzS,, SnS.
Wash and

(NH4)iS,.
Filter,
Analyze .
residue ac-
cordin|L to
SchemSli
II., A.
Analyze
filtrate ac-
xording to
Scheme
II. B.

Filtrate : Boil to expel H;S before proceeding
with the analjsb of Group 11. ppt. Add NHfC^
make alkaline with NH^OH, and completely ppt.
with H,S or (NH^jS ; filter.

- Beaidue:
AlCOH)„
Cr(OH)„
FeS, NiS,
^oS, MnS,
ZnS.

Analyse ac-
cord! i^ to

Filtrate is at once acidified with
acetic add and boiled to expel H,S,
and ihefi filtered. Make dear filtrate
alkaline with NH4OH, add
(NHj>,CO„ and-'filter.

BaCO,, SiCOs
-l-CaCO,.' '
Ana^ze ac-
cording to
Sdicme IV.

Filtrata will con-
tain Mg and the " al-
kalies." Divideinto
tno portions : | test
for Mg according to
Scheme "V; i test
for Na and K accord-
ing to Scheme V.

Test tax NH^ is made on a separate pMl^iiLaGcordiiig to Scheme V

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PART 11

THE ACIDS

It is customary to arrange the acids into groups according to
their deportment with two reagents, viz., BaClg and AgNOg.
Three groups are thus distinguished.

Group I. includes those acids whose barium or calcium salts
are insoluble in water; they are therefore precipitated from
neutral solutions by BaCI,. This group is divided into two
parts, namely: (a) Acids precipitated by BaCl^ from solu-
tions a«i/ with HCI, viz,, sulphuric acid (H^SO^) and hydrofluo-
silicic acid (HjSiFg); {d) Acids precipitated by BaCl^ from
neutral solutions only, viz., carbonic acid (HjCOg), sulphurous
acid (HjSOg), thiosulphuric acid (H^SjOg), phosphoric acid
(HgPO,), hydrofluoric acid (HF), oxaUc acid (HaCjO^), boric
add (HgBOa),* silicic acid (HaSiOB),t tartaric acid (HaC^H^O,),
arsenic acid (HgAsO^), arsenious acid (HjAsOg), and chromic
acid (HjCrOJ.

Group II. includes those acids whose barium salts are soluble
in water, but whose silver salts are insoluble in nitric acid ; they
are therefore precipitated by AgNOg from solutions acid with
nitric acid. These acids follow : —

Hydrochloric acid (HCI), hydrobromic acid (HBr), hydriodic
acid, (HI), hydrocyanic acid (HCN), hydrogen sulphide (HjS),
hydroferrocyanic acid [HjFe(CN)g], hydroferricyanic acid
[H8Fe(CN)8], thiocyanic acid (HSCN), and nitrous acid
(HNOj); the last is, however, only precipitated from moderately

• Orthoboric (eid (HtBOt) is here coniideTed u, lepreieDtktiTe of the acidi of
t MetuOicic add (HiSiOg) i« Uken u the type of the many lilicic acids.

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124 QUALITATIVE CHEMICAL ANALYSIS

concentrated solutions and is therefore also placed in the next
group.

Group III. includes those adds that are not precipitated by
either BaCl, or AgNOg, viz., nitric acid (HNOg), nitrous acid
(HNOa), chloric acid (HClOg), and acetic acid (HCjHgO,).

Sulphates

With the exception of the sulphates of lead, barium, strontium,
and calcium, all normal sulphates are soluble in water. Stiver
and mercury (-ous) sulphates are, however, difficultly soluble.
Nearly all basic sulphates are insoluble, but readily dissolve in
hydrochloric or nitric acids. Alkali and alkaline earth sulphates
are not decomposed when ignited gently in a closed tube, but at
higher temperatures more or less decomposition takes place.
The behavior of other sulphates on being heated varies with the
nature of the 'metal with which the SOj radical is united, some
resisting decomposition, while others are readily decomposed,
giving oflE SOj or SOj, or both, and leaving the oxide of the
metal.

Free sulphuric acid is recognized even in the presence of a
sulphate by its property, when concentrated, of removing the
elements of water from organic substances and leaving a charred
residue; thus, if to a solution containing free HjSO^ a little
cane sugar is added and the mixture is evaporated just to dry-
ness, preferably on a steam bath, a black residue will be 6\y
tamed.

I. Bariam Chloride precipitates white BaSO^,* insoluble in
water and in dilute acids even on boiling. From dilute solutions
a precipitate separates only on standing. Dilute HCl or HNOg

* From HG solntiom BaGi mty tlso precipitate BaSeOt and BaSiF«; the fonnet
is teadily distinguished (iota BaSOt and BaSiFg by the &ct that on boiling it with
concentrated HQ, chlorine is given off: —

BaSeO, + 4 HQ = Bad, + H,SeO, + + O, + HjO.

BaSiFt is easily recognized by its readiness to undergo deeompodtion when
hcftted with concentrated H3SO4 : —

BaSiF. + HjSO, = B^0« + +a HF + + SF*.

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THE ACIDS 125

should be added before tbe reagent in order to prevent the pre-
cipitation of chromates, sulphites, and carbonates. Strong acid
must not be used, for otherwise.a crystalline precipitate of BaCI^
or Ba(N03)2 may be obtained; these are, however, easily dis-
tinguished from BaSOj by their ready solution on diluting. For
further properties of BaS04, see reaction 4 under Barium.

2. Lead Acetate produces a white precipitate of PbSO^,
soluble in a hot concentrated solution of ammonium acetate or
tartrate.

3. Mixed with Na^COs free from sulphur compounds, and
heated on charcoal with the reducing flame of a blowpipe, all
sulphates are reduced to sulphides. If the fused mass is placed
on a silver coin and then moistened with a drop of water, a black
stain of AgjS will be produced : —

Na^S -I- 2 Ag -H HjO +0=^ AgjS + 2 NaOH.
This test is also given by other sulphur compoundi.

Fluosilicates

Hydrofluosilicic acid (HjSiFg) is formed by the action of sili-
con tetrafluoride (SiF^) on water : —

3 SiF^ + 4 H,0 = 2 HjSiFs -f- j H^SiO^.

If the silicic acid, which is formed at the same time, is filtered
off, the filtrate will contain an aqueous solution of hydrofluo-
silidc acid. Both tbe acid and its salts are decomposed on heat-
ing. On evaporating a solution of H^iFg, decomposition sets
in, according to the equation —

HaSiFg = fSiF^-|-t2HF.

With the exception of the potassium and barium salts, nearly
all fluosilicates are soluble in water.

BaSiFg, formed by adding BaClg to a solution of a fluosilicate,
is a white, crystalline, insoluble substance. Its solubility at
17° C. is I part in 3700 parts of water. As it is sparingly solu-
ble in HCl, it can be precipitated by BaCL, from solutions con-
taining this acid. For a method of distinguishing it from
BaSO,, see footnote, page 124.

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126 QUALITATIVE CBEMICAL ANALYSIS

Carbonates
Carbonic acid (H,COg) is a weak dibasic add which is only
known in solutioD. With bases it yields an important class of
stable salts known as carbonates. On ignition, the carbonates
of calcium and strontium are decomposed, while the normal
alkali carbonates are but slightly affected; ammonium carbon-
ate volatilizes on heating. Nearly all of the carbonates are
white, and, with the exception of the carbonates of the alkali
metals, all the normal salts are insoluble in water. The aqueous
solutions of the carbonates and dicarbonates of the alkalies
possess an alkaline reaction. Sodium dicarbouate, on ignition,
is changed to the normal salt with evolution of carbon dioxide
and water : —

2 NaHCOg = NajC08+ f H,0 + f COj.

1. All the adds, excepting HCN, decompose carbonates with
effervescence, due to the evolution of CO] ; the latter may be
recognized by its property of rendering turbid a drop of lime-
water held in the escaping gas : -^

CaCOg + 2 HCl = CaCla + HjO + f COj;
COa + Ca(OH)j - |CaCO, + HaO,
This constitutes the chief reaction for carbonates from an
analytical standpoint

2. Baiitim ta Caldum Chloride, when added to a solution of
a normal carbonate, gives a white precipitate of BaCO, or CaCOj.
The precipitate is soluble in carbonic acid as well as in all other
acids with the exception of HCN : —

CaCOg + HjCOg = Ca(HCOB>,.
From the solution of dicarbonate of calcium, CaCOg reprecipi-
tates on boiling : —

Ca(HC08)s = ICaCOg -«- HjO + f CO,.

3. SUver Nitrate precipitates white silver carbonate (AggCOg),
which, on boiling, changes to brown silver oxide (AggO): —

Ag,C0g = jAg30-|-fC0a.

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Sulphites
The aqueous solution of sulphur dioxide, known as sulphur-
ous acid, is a weak dibasic acid. When boiled it decomposes,
giving off SOj, which may be easily recognized by its odor.
Neutralized by bases, it forms sulphites, all of which are insolu-
hle or nearly so in water, with the exception of those of the
alkali metals. The solid salts, as well as their aqueous solutions,
readily oxidize on exposure to air, forming the corresponding
sulphates.

1. Barlam Chloride precipitates from /r««/m/ solutions white
barium sulphite (BaSOg), readily soluble in HCl and HNOg.
In practice, a residue of BaSO^ remains, due to the presence of
a small amount of sulphate originally present in the sulphite or
produced by the subsequent oxidation of the sulphite. If the
BaS04 is filtered off, the clear filtrate may be shown to contain
sulphurous acid by adding a little bromine or concentrated
HNOg and boiUng, when a white precipitate of BaSO^ will
form. The bromine or nitric acid oxidizes the sulphurous to
sulphuric acid, and the latter at once yields with the BaClj
present a precipitate of BaS04.

Free sulphurous acid is not precipitated by BaClg.

2. Hydrogen Sulphide, when passed into a solution of sul-
phurous acid, or a solution of a sulphite, acid with HCl, causes a
separation of sulphur with the formation at the same time of
pentathionic acid : —

5 H^ + 5 H,SO, = HjSjO, + j S S + 9 H,0.

3. Dilate H^^ or HCl, when added to a sulphite, decomposes
it with the evolution of SOj : —

NajSOg + 2 HCl = 2 NaCl + H,0 + f SO^

4. Silver Nitrate precipitates from neutral solutions white
AgjSOg, which, on boiling, is decomposed, with the separation
of gray metallic silver : —

AgaSOg + HjO = 1 2 Ag + HjSO,.

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128 QVAUTATIVE CHEMICAL ANALYSIS

5. Iodine Solatlons are bleached by sulphurous acid ; this is
due to the reduction of iodide to hydriodic acid : —

HaSOa + Ij + HiO:;;£2 HI + HjSO^.

6. Potasslnin Permanganate solution, acid with sulphuric acid,
is also decolorized by sulphurous acid: —

2 KMnOj + 5 HaSOg = KjSOi + 2 MnSO^ + 2 HjSO, + 3 HaO.
Since sulphur dioxide, which may be liberated from a sulphite
(see reaction 3), is much heavier than air, it may be decanted
into another test tube containing a small amount of exceedingly
dilute KMnO^ solution. Now, on thoroughly mixing the gas
and permanganate solution, the latter will be bleached.

7. Potassium Dlchromate, when added to sulphurous acid, is
reduced to a chromic salt; the reduction is accompanied by a
change in color to green : —

KaCraO^ + 3 HaSOj + HjSO, = KjSO* + CrgCSO,), + 4 HaO.

8. Stannous Chloride, when added to sulphurous acid or to
a hydrochloric acid solution of a sulphite, and the mixture
heated, reduces the sulphurous acid to H,S, which, after some
time, will precipitate the tin as stannic sulphide : —

3 SnCl, + HjSOg + 6 HCl = t HjS + 3 SnCl4 + 3 HjO ;
SnCl^ + 2 HjS = i SnSj + 4 HCl.

9. Sulphurous acid reduces arsenic acid (HgAsOJ to arseni-
ous acid (HgAsOj); the action is preferably conducted in a
closed, pressure bottle heated in a water batb. It also reduces
ferric to ferrous salts.

10- Sulphites, when heated with sodium carbonate on char-
coal, behave in the same way as sulphates (see reacdon 3).

Thiosulprates
Thiosulphuric acid _is unknown, for, when liberated from its
salts, it at once breaks down into SO^ S, and HjO. The chief
thiosulphate is the soolum salt (Na^SgOs), used extensively in
photography because of its property of dissolving the halides of
fftver.

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1. Dilate Hydrochloric Add decomposes all thiosulphates with
the evolution of sulphur dioxide and the separation of sulphur : —

NajSaOs + 2 HCl = 2 NaCl + H3O + f SO^ + \S.

This reaction serves to distinguish this class of salts from sul-
phites, which do not give a separation of sulphur when so
treated.

2. Silver Hltrate precipitates white silver thiosulphate, easily
soluble in an excess of sodium thiosulphate with the formatioo
of a complex salt : —

2 AgNO, + NajSaOg = | AgjSjOa + 2 Na^(08 ;
AgaSjOg + Na^SaOa = 2 NaAgSaOg.
Boiling decomposes the double salt with the separation of
silver sulphide and sulphur. Silver thiosulphate, almost as soon
as formed, owing to its instability, becomes yellow, then brown,
and jinally black, with the formation of AgjS : —

AgjSaOg + HjO = I AgjS + HjSOj.

Phosphates
Three phosphoric acids are known, viz., orthophosphoric acid
(HaPOj), metaphosphoric acid (HPOg), and pyrophosphoric acid
(HjPjOt). The most stable in solution, as well as the most
important of these, is the ortho-acid. The others are converted
into this form by boiUng with water, for example : —

HP08+H,0=HgP04.

Metaphosphoric acid, or the acetic acid solution of a meta-
phosphate, is distinguished from the other two by its cbarac*
. teristic property of coagulating albumen.

Pyrophosphoric acid and Its salts are formed by heating the
ortho- acid or its mono-hydrogen or mono-ammonium salts ;
thus: —

2 HgPO, = I HjO + H^PsOt ;
2 Na^HPOi = Na^PaO, + f HjO ;
2 NH^MgPOi = t H,0 -I- f 2 NHg + MgjPjO,.

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ijo QUAUTATIVE CHEMICAL ANALYSIS

With the exception of the alkali salts, all normal pyro- and
ortho-phosphates are insoluble in water. All of the phosphates
of the metals of Group IV. are soluble in acetic, hydrochloric,
and nitric acids. Those of the trivalent metals of Group III.
are insoluble in acetic but soluble in hydrochloric acid.

1. Baiinm Chloride (BaClg) precipitates from neutral solutions
of orthophosphates white BaHP04, soluble in acetic, hydro-
chloric, and nitric acids ; from the acid solution, ammonia pre-
cipitates the tertiary phosphate : —

BaClj + Na,HP04 = | BaHPO^ + 2 NaCl ;
BaHPO^ -I- 2 HCl = BaCl, -I- HgPO, ;
H8POj-»-3NH8 = (NH4)3POj;
2 (NH^^PO, -I- 3 BaClj = \ BaB(P04)j + 6 NH4CI.

2. Lead Acetate [Ph(^^sO))i] pi'ccipitates white lead phos-
phate, practically insoluble in acetic acid though soluble in
nitric acid : —

3 PKCaHgOa), + 2 NajHP04 =

\ Pbi(P04)i -I- 2 HCaHgOa + 4 NaC,HsO^

3. Silver Nitrate precipitates only from strictly neutral solu-
tions yellow silver phosphate (AggPOf), soluble in mineral acids ; *
it is also soluble in acetic acid and in ammonium hydroxide.

2 NaaHPO, + 3 AgNO, = | AggPO^ -f 3 NaNOg + NaHaPO^.

4. Magnesium ndxtnre (MgCl3+ NH^Cl -H NH^OH in slightex-
cess) precipitates from solutions of orthophosphates, white crystal-
line ammonium magnesium phosphate (NH^MgPOj-d H,0): —

MgCIj + NaaHPO^ -f NHg » \ NH^MgPO, -I- 2 NaCL

The precipitate is soluble in adds, including acetic add ; from
solutions of the latter ammonium hydroxide reprecipitates the
double phosphate (method of purification and separation from
AIPO4, which is insoluble in acetic add). The precipitate is
slightiy soluble in water, but is insoluble in 2.5 per cent,
ammonia water. From very dilute solutions, the precipitate

* With HO, B white predi^tate of AgCl is obttined.

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TBE ACIDS 131

separates only on standing; on ignition, it yields magnesium
pyrophosphate (Mg,PgO}). For further details concerning the
precipitate, see reaction 4 under Magnesiutn. Arsenates yield
a similar precipitate, but the latter is rendered reddish brown
on treatment with silver nitrate, due to its conversion into silver
arsenate (AgjAsOj).

5. Ammonlom Holybdate, when added to a warm nitric
acid solution of a phosphate, yields a canary-yellow precipi-
tate of ammonium phosphomolybdate of variable compositioii
[(NH4)gP04, ■ 12 MoOj]. Precipitation may be hastened by
heating and by having an excess of ammonium nitrate present.
The precipitate is soluble in excess of phosphoric acid or of
alkali acid phosphate ; hence, to secure complete precipitation,
a large excess of the reagent is necessary. It is also soluble in
alkalies, including ammonium hydroxide.

Arsenic acid yields a similar compound with this reagent, but
the precipitate forms more slowly and requires a higher tempera-
ture for its complete precipitation.

This reaction affords a means of quantitatively separating
phosphoric acid from the metals with which it may be combined.

6. Ferric Chloride, when added to a soluble phosphate not too
strongly acid, yields a. buff-colored precipitate of ferric phos-
phate (FePOj) : —

FeClg + NajHPO^ = \ FePO^ -I- 2 NaCl -H HCl.

As ferric phosphate is soluble in hydrochloric acid, the pre-
cipitation by ferric chloride in the above reaction is never com-
plete; by adding an excess of sodium acetate, however, the
hydrochloric acid is replaced by acetic acid, in which FePO^ is
insoluble, and, as a consequence, precipitation is rendered com-
plete:—

Fea8+Na,HP04-l-NaCjH,0,=3 NaCl-t- iFePOj-l-HCjHgO,.
This reaction is utilized in removing phosphoric acid from
solutions.

7. Metallic Tin, when added to a nitric add solution of a
phosphate, precipitates the phosphate as stannic phosphate, the

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133 QUALITATIVE CBEMICAL ANALYSIS

excess of the tin separating at the same time as insoluble tneta-
stannic acid. This reaction, like the one above, may be em-
ployed for the separation of the PO^ radical from the metals.

Fluorides

Hydrogen fluoride, the water solution of which is hydrofluoric
acid, at 19.5° C. is a colorless, highly corrosive liquid. Its aque-
ous solutions attack the skin, producing painful sores ; it must
therefore be handled with care. As its chief property is its
abiUty to etch glass, it must be kept in ceresine, hard rubber, or
platinum vessels. With bases, it yields salts, known ^^ fluorides.

The fluorides of the alkali metals, with the exception of that of
lithium, are soluble in water. Those of the alkaUne earth group
are either insoluble or sparingly soluble in water. The fluorides
of Cu, Pb, Zn, and many other heavy metals, are only slightly
soluble, while those of Al, Ni, Co, Ag, Sb, and Sn (-ous) dissolve
readily.

I, Concentrated H^SO^ decomposes most fluorides with the
liberation of hydrogen fluoride : —

(i) CaFj+HjSOi^lCaSOi + fzHF.

The reaction proceeds more rapidly if the mixture is heated.
The HF may be recognized by its abiUty to etch glass (see re-
action 2),

If the reaction is carried out in a test tube, the hydrofluoric
acid which is set free attacks the glass, with the evolution of
silicon tetrafluoride : —
(2) Na^Si^T - CaSigOT -I- 28 HF =

*^ 2 NaF -«- |CaF, -I- f 6 SiF^ -H 14 HjO.

When brought in contact with water, silicon tetrafluoride reacts
according to the following equation : —

(3) 3 SiF^ + 4 HjO = 2 HjSiFj -H iH^SiO^.

The above three reactions may be utilized in testing for a fluo-
ride. One need only heat the substance in a test tube with
concentrated HjSO^ and then hold in the escaping vapors a

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TEE ACIDS 133

drop of water held on the loop of a platinum wire. In the pres-
ence of a fluoride, the " water bead " will become turbid owing
to the formation of gelatinous silicic acid. The test may also
be carried out in lead or platinum vessels, if the fluoride is first
intimately mixed with ignited silica (SiOg) before the treatment
with concentrated H,SOj.

The reactions are as follows : —

2CaFa + 2 HaS04-.|2CaS04 + t4HF;
4HF + SiOa = fSiF, + 2 H,0;
3 SiFj + 4 HjO = 2 HaSiFg + 4 H^SiO,.

3. The Etching Test This test, as explained above, is based
on the property possessed by hydrofluoric acid to dissolve SiOj
or glass. In a platinum crucible or lead dish, mix, with the aid
of a piece of wood, some of the powdered substance with concen-
trated sulphuric acid. Cover with a watch glass that has been
coated on the convex side with paraffine and through which
some characters have been scratched. Put a little water on
the upper concave side of the watch glass to prevent the par-
afRne from melting during the heating, and gently beat the
crucible or dish, preferably on a water bath. After some time,
remove the watch glass, warm it, and wipe the parafhne o3. If
a fluoride is present in the substance under examination, the
glass will be corroded or etched in those places where the glass
has been exposed to the liberated hydrofluoric acid. It is evi-
dent that this test is inapplicable in the presence of silicates.
Anhydrous HF does not etch glass.

3. Calcium Chloride, added to an aqueous solution of a fluo-
ride, gives a white gelatinous precipitate of calcium fluoride
(CaFa), soluble with difficulty in HCl and HNOg, but practi-
cally insoluble in acetic acid. From the acid solution of calcium
fluoride, ammonium hydroxide does not reprecipitate the fluo-
ride, because of the solubility of CaFj in ammonium salts.

4. Fusion with Sodium Carbonate only partially decomposes
CaFj. In the presence of silica, however, the decomposition
may be rendered complete.

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134 QUAUTATIVE CEEMICAL ANALYSIS

Oxalates

With the exception of those of the alkali metals, magnesium
and chromium, nearly all the oxalates are insoluble or sparingly
soluble in water ; they all are soluble in mineral acids and in
many cases in an excess of alkali oxalate with the formation of
double salts.

I. Barinm Chloride precipitates white barium oxalate(BaC304),
soluble in oxalic and acetic acids.

3. Caldam Sulphate or Caldam Chloride precipitates white
crystalline CaCjO^, insoluble in oxalic and acetic acids, and in
ammonium oxalate, but soluble in hydrochloric acid. As
CaCjOj is one of the most insoluble of the oxalates, CaSO^ is
an excellent reagent for the detection of this acid.

3. Concentrated Sulphuric Add, when added to an oxalate in
the sohd state, decomposes it with the evolution of CO and
COj: —

H,C,0^ + HaSO< = HjO + HjSO^ + fCO +tCOa.
If the mixed gases are passed through limewater or sodium
hydroxide, the CO3 will be absorbed and the escaping CO may
be recognized by the characteristic blue Same with which it
bums.

4. Potassium Permanganate Solution, when added to a hot
sulphuric acid solution of an oxalate, is bleached because of its
reduction to a manganous salt, the oxalic acid bemg oxidized at
the same time to CO, and water: —

2 KMnO, + 3 HaSOj + S HjCaO^ =

KaSO* + 2 MnSOj + 8 H,0 + f 10 CO,.

5. Behavior of Oxalates on Ignition. At a red heat, all oxa-
lates are. decomposed with the evolution of CO and COg. The
oxalates of the alkalies and alkaline earths are converted by
ignition into carbonates with little or no carbonization. Mag-
nesium oxalate yields MgO when heated. All other oxalates
leave either a residue of metal or an oxide, depending upon the
ease with which the oxide is reduced.

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THE ACIDS 135

An oxalate may be decomposed by evaporating it with a
mixture of HjSO^ and HNOs until SOg fumes are given off;
any organic matter present will also be destroyed at the same
time.

Borates

BoroD forms three acids, namely, orthoboric acid (HgBOg),
metaboric acid (HBOg), and tetraboric acid (HaB^O^); the last
two may be obtained from the first by careful heating. Salts of
the ortho-acid hydrolyze in a water solution, so that the salts of
boric acid we are concerned with are either of the meta- or pyro-
type. Borates of the alkali metals alone are soluble in water,
yielding solutions which have an alkaline reaction owing to par-
tial hydrolysis ; all other borates are either insoluble or spar-
ingly soluble in water, but are readily soluble in mineral acids
and in ammonium salts.

I. Turmeric Paper Test. If a piece of turmeric paper is
dipped into a solution of a borate slightly acid with HCl, and
the paper is then dried by placing it on a watch glass and heat-
ing the latter on a water or steam bath, the paper assumes a
reddish brown color. If the paper is now moistened with a
drop of caustic soda solution, the color changes to a greenish
black.

3. Barium Chloride precipitates from concentrated solutions
flocculent barium metaborate, soluble in excess of barium chlo-
ride, in ammonium chloride, and in acids: —

NaaB^Ot + BaClj + 3 HjO = 2 NaCl -|- 2 HgBO, -I- 1 BaCBOa)^.

3. Calcium Chloride gives with borates reactions precisely
similar to those produced by BaCl,.

4. Silver Nitrate precipitates from cold concentrated solutions
white silver metaborate (AgBOa), soluble in ammonium hydrox-
ide and nitric acid; warming converts it into brown silver oxide
(Ag,0).

5. Flame Tests. Free boric acid and some of its volatile
compounds, e.^., the fluoride (BF^its esters, as (CH,)gBO| and

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136 QUALITATIVE CHEMICAL ANALYSIS

(C3H,)gBOg, when brought into the bunsen flame, impart to
it a characteristic green color.

6. CODceatrated Solphorlc Acid, when added to a borate, de-
cumposes it with the liberation of free boric acid (HjBOj). The
test depending upon this and the above reactions is carried out
by making a paste of the substance with concentrated HaSO^,
taking up some of the mixture on the loop of a platinum wire,
and holding it in the flame, when, if a borate is present in the
substance being examined, the characteristic green color will be
observed. This test does satisfactorily for most borates. For
silicates containing boron, which are not decomposed by con-
centrated HjSOj, it is necessary to mix the mineral with a little
calcium fluoride before adding the sulphuric acid ; under these
conditions, volatile boron fluoride (BFg) is formed, which, when
brought into the bunsen flame, colors it green.

7. Concentrated HgSO^ and Alcohol. If concentrated suiphuric
acid is added to a borate and then a little methyl or ethyl alco-
hol, and ^he mixture is stirred and lighted, the resulting flame
will be found to be green at its borders, due to the formation of
volatile methyl or ethyl borate : —

HjBOs + 3 C3H5OH 5t 3 H,0 + 1 (C:jH5)gB0j.

The concentrated HjSO, performs the double function of
liberating the boric acid and absorbing the water formed in the
above reversible reaction, thus causing the latter to proceed
from left t6 right.

8. Beharior on Ignition. Borates of the alkali metals, when
heated, swell up (escaping of water), and finally fuse with the
formation of a colorless glass; the latter, possessing as it does
an excess of acid oxide, readily unites with metallic oxides on
heating, with the formation of metaborates (borax beads) having
characteristic colors. Thus, with cobalt oxide or any cobalt
compound we obtain

CoO + NajBjOT = 2 NaBO, + Co(BOi)a.

The cobalt metaborate is blue.

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THE ACIDS 137

Silicates

Silica (SiOj), the anhydride of silicic acid, occurs abundantly
in a more or less pure state in nature as quartz, rock crystal,
flint, agate, sand, etc. It is insoluble in water and in all acids
with the exception of hydrofluoric acid ; the latter dissolves it
with the formation of gaseous silicon tetrafluoride (SiF^) : —
SiOj + 4 HF = f SiFj +2 H3O.

To expel silica completely with HF, the presence of concen-
trated HjSO^is necessary. When silica is fused with sodium
carbonate and the mass is extracted with water, a solution of
sodium silicate is obtained : —

SiOj + NajCOa = NaaSiOg + \ COj.

AH silicates are insoluble in water with the exception of those
of sodium and potassium, which are soluble in water in the
presence of free alkali.

I. If to a solution of sodium or potassium^ silicate, hydro-
chloric or nitric acid is added until an add reaction results, part
of the siUcic acid will separate out as a gelatinous precipitate,
while the rest will remain in solution in the form of a hydrosoi : —
NajSiOs + 2 HCl = 2 NaCl -«- 1 HaSiOg.

If the sodium silicate solution is very dilute, the silicic acid set
free may remain entirely in solution.

Precipitated silicic acid is somewhat soluble in water and in
acids, and is readily soluble in alkaU hydroxides and carbonates.

If an acid solution of an alkali silicate, which may contain
more or less of precipitated silicic acid in suspension, is evapo-
rated to dryness on a boiling water bath, the precipitated, as
well as the dissolved, silicic acid loses water and becomes insolu-
ble in acids ; therefore, on extracting the dried residue with hy-
drochloric acid and filtering, practically all the silicic acid (about
99 per cent.) will be left on the filter in a more or less dehy-
drated state. The more complete the dehydration, the more
insoluble does the resulting silicic acid become. This property
of silicic acid of becoming insoluble in adds on dehydration is

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138 QVAUTATIYE CHEMICAL ANALYSIS

of great analytical importance, since it enables the analyst,
early in the analysis, to completely separate the silicic add
from the metals with which It was originally combined.

2. Ammonlmn chloride or ammoniom carbonate, when added
to a solution of alkali siUcate, causes a precipitation of meta-
silicic add : —

Na,Si08+2NH^Cl+2HjO = |HaSi03+2NaCl + 2NH40H;
Na,SiOg+(NHJaCOB+2HjO = iHjSi03+Na,COg+2NH40H.

3. Bariom Chloride precipitates white BaSiO^ soluble in
acids.

4. SilTer Nitrate precipitates yellow Ag^SiO,, soluble in acids
and in ammonium hydroxide.

5. Ammonium Holybdate solution containing an excess of
nitric add yields, with solutions of silicates, a yellow solution.
On heating in the presence of much NH^Cl, a canary-yellow
predpitate is produced.

6. Sodium Metaphosphate Bead Test. When a sili£:ate is
fused in a metaphosphate bead prepared from microcosmic salt
(NHjNaHPO,), the bases are dissolved to a transparent bead,
while the silica in the form of a " skeleton " of the original mass
remains undissolved as an opaque body : —

CaSiOg + NaPOg = CaNaPO^ + SiOj.

Treatment of Insoluble Silicates

(fl) Silicates decomposed by Acids (not including hydrofluoric

acid). The finely ground silicate * is heated in a casserole with

* Powdering Mineiala. Since sabstances aie more re&diif soluble in a stale of

fine powder than in the fonn of lumps, the process of powdering is always resorted to
before the analysis of minetals, slags, and ores is begun. This is accomplished by
first wrapping up in a clean towel a number of selected specimens of the sabstance,
placing the latter on a plate of hard steel and breaking them iip with several sharp
blows from a hard steel hammer. The resulting mixture of powder and coarse parti-
cles is then introduced into a diamond steel mortar, in small portions at a time, and
crushed to a coarse powder; the latter is then thoroughly miied, and about two
grams or more are reduced to an extremely fine state of division by grinding in an
agate mortar until Che entire quantity passes through a loo-mesb sieve.

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THE ACIDS 139

ctmceiitrated HCl " and is boiled until decomposition is com-
pleta As a result of the action of the add, part of the silicic
acid separates in the gelatinous form. The mixture is then
evaporated to dryness, preferably on a steam bath, and the
silica is completely dehydrated by beating the nearly dry mass
in an air oven maintained at 120° C. until no more acid fumes
are given off. The dried residue is first treated with 10 cc. of
concentrated HCl and heated to dissolve the bases, some of
which may have been rendered difficultly soluble by the dehy-
dration process; water is then added, the mixture is heated
again with stirring, and finally is filtered. The filtrate will con-
tain all of the metals in the form of chlorides. The residue
will contain practically all of the silicic acid and may be con-
taminated with small amounts of the bases, chiefly iron and
aluminum as oxides. To test the purity of the siUcic acid, the
precipitate and a portion of the filter retaining the precipitate
are placed in a platinum crucible, moistened with a little con-
centrated ammonium nitrate solution to facilitate the combus-
tion of the filter, and ignited until all of the paper is consumed.
The crucible is then carried to the hood, placed on a pipestem
triangle, and is treated with a few drops of concentrated H^SOj
and about $ cc. of hydrofluoric acid. It is then gently heated
to dryness and Anally ignited. By this treatment all the siUcic
acid will be driven off as SiF^. Any residue is treated accord-
ing to page 197 for insoluble substances.t

(6) Silicates which are slightly or not attacked appreciaUy by
acids in the above treatment are decomposed by fusing them
in a platinum crucible, unless reducible metals are shown to be
present, with ten times their weight of a mixture of sodium and
potassium carbonates until the mass is in a state of quiet fusion.
By this treatment, the silica will be converted into sodium
silicate, while the bases will be variously converted into car-
bonate, oxide, or metal, depending upon their nature. After
cooling, the crucible with its contents is placed in a casserole or

" When melsls of the fii« group we known to be present, it is preferable to use
t The residue may comiit of AliOi, FcgOi, or B4SO4, or of all three sabsttoce*.

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I40 QUALITATIVE CHEMICAL ANALYSIS

evaporating dish, and is treated with an excess of hydrochloric
acid.* The latter takes the bases into solution and at the same
time decomposes the alkali silicate with a partial precipitation
of silicic acid. The mixture is then evaporated to dryness,
dehydrated at 120" C, extracted with hot concentrated add,
diluted with water, and the silicic acid is filtered off and purified
as already outlined. The filtrate is examined for bases and acids
except those removed by the above treatment (see page 167).

(e) Decomposition of Silicates with Hydroflooric Acid, (/nder
a hood, treat about one gram of the finely powdered mineral
contained in a platinum crucible or dish with about 10 cc. of
hydrofluoric acid and 2 cc. of concentrated H,SOj, and evaporate
on a hot pkte until SOg fumes are evolved. By this procedure,
the silicate will be decomposed and the metals are left as
sulphates.

Treatment for the Detection of Alkalies In Silicates. If
undecomposed by acids, except hydrofluoric, apply J. Lawrence
Smith's method, which is given under the head of " Insoluble
Substances." The hydrofluoric acid method is also suitable for
the detection of the alkalies in insoluble silicates.

Tartrates

Solubilities. The normal tartrates of the alkali metals, as
well as those of aluminum and ferric iron, are soluble in water ;
nearly all others are insoluble in water, but are soluble in hy-
drochloric and nitric acids, and for the most part are soluble in
an excess of alkali tartrate with the formation of double salts.

I. Concentrated Salphuric Acid, when added to a tartrate and
the mixture is heated, causes a charring with the evolution of
SOj.

' a. Silver Nitrate does not react with free tartaric acid, but
from solutions of normal tartrates it precipitates white curdy
silver tartrate (AgaC^H^O,), readily soluble in nitric add and
ammonium hydroxide. If the tube containing the ammoniacai
solution of , silver tartrate is heated gently, preferably in a boil-

' If metall of Group I. are known to be present, it is pieferable to we nitric mdd.

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TEE ACIDS 141

ing water bath, a deposit of silver forms on the sides of the tube
in the form of a mirror.

3. Calcium Chloride, added in excess to a concentrated solution
of a neutral tartrate, precipitates white crystalline calcium tar-
trate (CaCjHiOg), soluble in acids, including acetic acid; the
precipitate is soluble in cold caustic soda free from carbonate,
from which, on boiling, CaCjHjOg reprecipitates in a gelatinous
form which redissolves on cooling- The precipitation of cal-
cium tartrate is interfered with by the presence of ammonium
salts. If CaClg is not added in excess, a white amorphous
precipitate forms ; this dissolves in excess of the normal tartrate
with the formation of a double salt.

4. Potassium Salts, when added to a neutral solution of a tar-
trate, give no precipitate ; if, however, the resulting solution is
rendered acid with acetic or citric add, a crystalline precipitate
of " cream of tartar " forms at once or after some time, depend-
ing upon the concentration of the tartrate solution. For prop-
erties of this salt, see reaction 2 under Potassiutn. Free tartaric
add or sodium acid tartrate solutions of moderate strengths give
an immediate precipitate with potassium salts.

5. SehavloT OB Ignition. Tartaric add and tartrates, when
heated, decompose with the evolution of inflammable vapors
possessing the odor of burnt sugar ; a carbonaceous residue is
left at the same time, consisting of carbon in the case of tartaric
add or of a mixture of carbon and alkali carbonate in the case
of alkali tartrates. The heavy metal tartrates on heating may
leave a residue consisting of the oxide of the metal or of the
metal itself. -

Chromates

Chromic add and chromates have already been mentioned in
connection with the metal chromium (see page 74). They are
all red or yellow.

Solabillties. The chromates of the alkalies, magnesium and
caldum, are soluble in water. Nearly all the others are insoluble ;
most of these dissolve in nitric acid. The acid solutions are

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143 QVAUTATIVE CBEMICAL ANALYSIS

always red, owing to the presence of a dichromate. The color
of chromates, even in vety dilute solutions, is easily visible, and
hence, in the absence of other colored substances, furnishes a
delicate test for their presence. For a discussion of the reduc-
tion of chromates to chromic salts and of the oxidation of the
latter to chromates, see under Chromium, pages y6 and 74.

1. Barium Chloride precipitates yellowish white barium chro-
mate (BaCrO^), difficultly soluble in water but soluble in hydro-
chloric and nitric acids. For other properties, see reaction 5
under Barium.

2. Lead Acetate precipitates from neutral or acetic acid solu-
tions yellow lead chromate (PbCrO^) ; —

Pb(CaHgOa)j + NaaCrO, = | PbCiOi-J- 2 NaCjHaOj.
This is practically insoluble in water, acetic acid, and ammonium
hydroxide, but is soluble in caustic soda solution, from which
acetic acid reprecipitates the chromate ; it is also soluble in
nitric acid-

3. Silver Nitrate precipitates from strictly neutral solutions
purplish red silver chromate : —

2 AgNO, + Na^CrO, = j AgjCrO, + 2 NaNOg.
Silver chromate is readily soluble in nitric acid and ammo-
nium hydroxide. From slightly acid concentrated solutions a
reddish brown crystalline precipitate of AgjCr307 is formed
which possesses about the same soluhihties as AgjCrO,: —

2 AgNOa + KjCrjO, = lAgjCrjO^ + 2 KNOg.
The chromates of silver are readily converted into the chloride
by treatment with HCl.

4. Potassium Iodide, when added to a dichromate or a nitric
acid solution of a chromate, is oxidized with the liberation of
iodine ; a drop of CSj, when added and shaken with the mix-
ture, acquires a violet color, due to the extraction of iodine.
The chromic acid is reduced at the same time.

5. Ethyl Alcohol (CjHgOH), when added to a chromate solu-
tion acidified with HCl or H3SO4, and the mixture is boiled.

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THE ACIDS 143

causes a reduction of the chromate to a chromic salt, as indi-
cated by a change in color of the solution from orange-red to
green. The alcohol is oxidized at the same time to acetalde-
hyde : —

KjCfjOt + 3 CaHgOH -I- 8 HCl =

2 CrClg -I- 7 HaO -H 2 KCl + f 3 CHgCHO.

This method is frequently used to reduce chromates to chromic
salts before treating a solution containing a chromate with HgS.
For the equation for the reduction of chromates by concentrated
HCl, see page 76.

6. Hydrogen Dioxide Test. If to a mixture consisting of 5 cc.
of dilute hydrogen dioxide solution, slightly acid with dilute sul-
phuric acid, and 2 cc. of ether, a little chromate solution is
added, and the mixture is shaken, the ether layer will acquire
an intense blue color, due to the presence of some such additive
compound as CrOg ■ HjOj, which, however, is very unstable.
One part of K^CrOj in 40,000 parts of water is said to be the
sensitiveness of this reaction.

7. Insoluble Chromium ComiKmnds, when fused with sodium
carbonate to which a little potassium chlorate has been added,
and the mass is extracted with water, will yield an aqueous
solution containing the chromium as chromate, while the resi-
due will contain the other metals. (Note, however, the conduct
of Manganese under similar conditions.)

GROUP II

This group comprises those acids which yield with silver
nitrate precipitates insoluble in nitric acid. BaCl^ does not
precipitate them.

Chlorides

Solubilities. All chlorides are soluble fti water with the
exception of those of silver, copper (-ous), and mercury (-ous).
The oxychlorides of mercury (-ic), bismuth, and antimony are
also insoluble. Lead chloride is sparingly soluble in cold water.
The normal chlorides of bismuth and antimony require the
presence of free acid to keep them in solution. All insoluble

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144 QUAUTATIVE CHEMICAL ANALYSIS

chlorides dissolve in aqua regia with the exception of silver
chloride. Fusion with sodium carbonate transposes • all insolu-
ble chlorides : —

2 AgCl + NaaCOg = 1 2 Ag + 2 NaCl + f COj + f O.

The chlorides of barium, sodium, and potassium are practi-
cally insoluble in concentrated hydrochloric acid.

I. Silver Nitrate precipitates from nitric acid solutions, white,
curdy silver chloride (AgCI), which darkens on exposure to
light; the precipitate is soluble in ammonium hydroxide and
carbonate, sodium thiosulphate, and potassium cyanide.

Besides the fusion method with sodium carbonate above men-
tioned, silver chloride may be tested for chlorine by treating it
with zinc and sulphuric acid, and allowing the action to con-
tinue for several minutes. If, now, the mixture is filtered, the
filtrate will contain the chlorine in the form of ZnCl, : —

2 AgCl -I- Zn = ZnCLj -H 1 2 Ag.

3. Lead Acetate precipitates white lead chloride (PbC^). For
its properties, see reaction 1 under Lead.

3. Concentrated H3SO4 and UnO,, when added to a chloride,,
and the mixture is heated, oxidize the chloride, with the evolution
of chlorine ; the latter is recognized by its color and odor as-
well as by its ability to bleach moist litmus or indigo paper : —

MnOa-l- 2 NaCl + 2 HaSO^ = MnSO^ + NajSO^ + 2 HaO + f Clj.

4. Potassinm Dichromate and Concentrated Solpharic Acid>
If a dry mixture of a chloride and powdered KjCr^Oj is treated
with concentrated H^SO^ and heated gently, chromyl chloride
(CrOaClj), a reddish brown gas, will be evolved : —

KjCraOj +4 NaCl 4- 6 H^SOi ==

\ 2 CrOjClj -I- 2 KHSO, + 4 NaHSO^ -h 3 HjO.

* When an insolnble lalt is treated with lodium carbonate, whereby the acid
tadical ii comerted into a soluble sodium salt, th« compoond is said to be trantptaed^

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THE ACIDS I4S

If the gas is absorbed by ammonium hydroxide, the latter
will be colored yellow owing to the formation of ammonium
chromate : —

CrOaCIj + 4 NH^OH = (NH()3CrOj + 2 NH^Cl + 2 H,0.

The presence of chromic acid in the ammonium hydroxide
solution may be shown by rendering it acid with acetic acid and
adding Pb (CjH803)j, when a yellow precipitate of PbCrO, will
be obtained.

This test for a chloride is of special value, for by its means
chlorides may be detected in the presence of bromides. Iodides,
if present in not too large amounts, do not interfere. The reac-
tion with the bromide is as follows : —
6 KBr + KaCrjOj + 1 1 HaSO^ =

f 3 Br j+ 8 KHSO. + CrjCSO,), -I- ; HjO.
The liberated bromine does not color the ammonium hydroxide,
and hence does not interfere with the test Iodides behave in
the same way as bromides.

Bromides

Solubilities. All bromides are soluble in water with the
exception of those of silver, mercury (-ous), copper (-ous), and
lead, the last being only sparingly soluble in cold water. Solu-
ble bromides of the heavy metals are easily transposed by boil-
ing with sodium carbonate solution. The insoluble bromides are
tested for the halogen by fusion with NaCOg, extracting the
melt with water, and filtering. The filtrate will then contain
the bromide as NaBr.

I. Silver Nitrate precipitates yellowish white silver bromide
(AgBr), which darkens on exposure to light; it is insoluble in
nitric acid and in cold ammonium carbonate ; it dissolves with
difficulty in cold ammonium hydroxide, but easily in KCN and
NajSjO,. Silver bromide may be decomposed by Zn and sul-
phuric acid in the same way as indicated for AgCl.

3. Chlorine Water, when added in small amounts to a solution
of a bromide, decomposes it with the liberation of bromine. If

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146 QVAUTATIVE CHEMICAL ANALYSIS

a few drops of carbon disulphide (CSg) or chloroform (CHClgX
in which bromine is soluble, are added, and the mixture is
shaken, the CSj or CHClg will acquire a yellow or reddish color,
depending upon the amount of bromine present. The test is
exceedingly sensitive ; i part of bromine in locxi parts of water
suffices to give a distinctly visible result.

KBr + a = KCI+Br.

Care must be exercised in performing the test to add the
chlorine water one drop at a time, and to shake after each ad-
dition; for, if an excess is added, colorless bromine chloride
(BrCl) may form.

3. Potassinm Dlchromate, in the presence of cold dilute sul-
phuric acid, does not liberate bromine from bromides (distinc-
tion from iodides).

4. Concentrated H1SO4, when added to a bromide, and the
mixture is heated, causes the liberation of bromine with hydro-
bromic acid.

5. Concentrated H^SO^ and Hn<^, when added to a bromide,
and the mixture is heated, causes the liberation of bromine ; the
latter is recognized by its color, odor, and by its property of
turning starch yellow and starch-iodide paper blue.

6. Potassium Nitrite, when added to a bromide acidified with
dilute sulphuric acid, does not liberate bromine (distinction from
iodides).

7. Potassium Permanganate, when added to a bromide solu-
tion acid with sulphuric acid, and the mixture is boiled, causes
the liberation of bromine, recognizable by its odor, color, and by
its ability to turn starch-iodide paper blue.

8. Nitric Add decomposes bromides, with the exception of
AgBr, on heating, with the liberation of bromine : —

6 KBr-l- S HNOg = ^ 3 Br^ + 6 KNOj + f 2 NO -»- 4 H,0.

Iodides

SoluMUties. With the exception of Hglj, Hgl, Agl, Cul, and

the sparingly soluble Fbly all iodides are soluble in water.

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TBE ACIDS 147

Some of the insoluble ones dissolve in an excess of alkali iodide
witlk tlie formation of double salts. Soluble iodides of the heavy
metals ^e best tested for the halogen by first transposing by
boiling with sodium carbonate solution. The insoluble iodides
— like the insoluble chlorides and bromides — are best trans-
posed by fusion with sodium carbonate.

1. Silver Nitrate, when added to a. solution of an iodide, pre-
cipitates yellow amorphous silver iodide (Agl), insoluble in
nitric acid, and only very sparingly soluble in ammonium hy-
droxide and cold ammonium carbonate (distinction from chlo-
rides). It is soluble in potassium cyanide and sodium thiosul-
phate solutions. Silver ioidide may be decomposed by Zn and
HjSOj in the manner indicated for AgCl and AgBr.

2. Concentrated H^SO^ acting alone on an iodide, yields hy-
driodic acid and iodine, mixed with various reduction products
of sulphuric acid, depending upon the temperature and the rela-
tive proportions of acid and iodide.

3. Concentrated H3SO4 and Kanganese Dioxide, when added to
an iodide, and the mixture is heated, liberate iodine. The reac-
tion is similar to those in which Br and CI are set free by the
same reagents.

4. Chlorine Water, when added drop by drop to a solution of
an iodide, decomposes it with the liberation of iodine : —

KI-t-Cl=KCl-l-I.
The free iodine may be recognized by shaking the mixture
with a few drops of CSj or CHCig; the latter solvents will ex-
tract the iodine and acquire a reddish violet color. Free iodine
may also be identified by the blue colored compound it yields
when treated with starch paste. Inliherating iodine with chlorine
water, care must be taken to avoid adding an excess, otherwise
the liberated iodine will be oxidized to colorless iodic acid : —
I, -t- 6 H,0 -I- 5 Cla = 10 HCl-l- 2 HlOg.

5. Potasslom Nitrite, when added to a solution of an iodide
acid with sulphuric acid, causes the separation of iodine, recog-
nized by coloring CSg violet or starch paste blue.

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148 QVAUTATIVE CHEMICAL ANALYSIS

In carrying out the starch-iodide reaction, it is important to
have the iodine solution very dilute ; if it is at all concentrated,
a nearly black precipitate, instead of a fine blue coloration, will
be obtained. Potassium nitrite has an advantage over chlorine
as an iodine Uberator, as an excess does not hinder the reaction.

6. Cupric Salts, when added to a solution of an iodide, yield
a dirty brown precipitate of cuprous iodide (Cul) ; at the same
time iodine is set free : —

2 CuS04+ 4 KI - 2 KjSO,-!- 1 2 Cul + 1 2 I.

7. Ferric Salts also liberate iodine from iodides, being at the
same time reduced to the ferrous state : —

Fea( 504)3 + 2 KI = 1 13 + 2 FeS04 + KaS04.

8. Potassinm Dlchromate, when added to an iodide solution
add with sulphuric acid, causes iodine to be set free : —
K,CraO,+6KI-(-7H3SO4=4KaS04+Cra(SO4)8+|3l|+7H,O.

In all of the above cases the liberated iodine may be detected
by shaking the mixture with one cc, of CHCij or CSj, which
acquires a violet color.

9. Hercttiic Chloride, when added to an iodide solution, pre-
cipitates scarlet mercuric iodide (Hgl,), soluble in an excess of
alkali iodide : —

HgCl, -«- 2 KI - 1 Hgl, -H 2 KCI ;
HgI, + 2KI=.KaHgl4.

Cyanides

SolnbilltieB. The alkali and alkahne earth cyanides and mer-
curic cyanide are soluble in water ; nearly all others are insol-
uble. The cyanides of the heavy metals dissolve in an excess
of alkali cyanide with the formatiou of complex double salts.

Heated with exclusion of air, the cyanides of the alkalies and
alkaline earths fuse without decomposition. In contact with
air, they oxidize with the formation of cyanate : —

NaCN-l-O-NaCNO.

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TEE ACIDS 149

It is in consequence of the readiness with which they oxidize
that the reducing power of cyanides is due. The cyanides of
the heavy metals when heated in a closed tube undergo decom-
position, the products varying with the nature of the metal : —
Hg(CN)i,-Hg + t(CN),;
Pb(CN)B=Pb + 2C + tNa.

Cautioh : AJl texts for cyanides which involve the evolution of
a gas should he performed under the hood.

The cyanides of the noble metals on heating break up into
the metal and cyanogen gas. By this means, the cyanides of
silver and mercury allow themselves to be readily detected.
Mercuric cyanide differs in many respects from the other water-
soluble simple cyanides. It does not yield a precipitate with
silver nitrate and is not decomposed by cold dilute sulphuric
acid ; it is, however, decomposed by HgS with the precipitation
of -mercuric sulphide and the production of HCN.

1. Silver Nitrate, when added to a simple cyanide, excepting
Hg(CN^, yields a white precipitate of silver cyanide (AgCN),
easily soluble in excess of alkali cyanide with the formation of a
double cyanide : —

AgCN + KCN = KAg(CNV
AgCN is also soluble in ammonium hydroxide and in sodium
thiosulphate, but is insoluble in nitric acid. On ignition, it is
decomposed with the evolution of cyanogen gas and the separa-
tion of silver : —

2AgCN=42Ag + f(CNV

2. Snlphtuic Acid, dilute, when added to a solution of a cya-
nide [except Hg(CN),], decomposes it with the liberation of
HCN, readily recognized by its odor. If the dilute acid is
heated, it is capable of decomposing the insoluble cyanides.
If the acid is concentrated and hot, it will attack all cyanides
whether simple or complex ; —

Co<CN)a + 2 HjSO, + 2 HjO = C0SO4 + ( NH4)jS04 -|- f 2 CO ;
K4Fe(CN>, + 6 HjSO^ + 6 H,0 =

FeS04 + 2 K,S04-H 3 (NHASO, -h f 6 CO.

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ISO QUAUTATIVE CSEUICAL ANALYSIS

The above equations, which are typical, show that the metals
are converted into sulphates, that carbon monoxide is produced,
and that all the nitrogen is converted into ammonium sulphate.

3. Formation of Ferrocyanide. If a solution containing an
alkali cyanide is made strongly alkaline with sodium hydroxide
and a little ferrous sulphate and ferric chloride are added, and
the mixture is gently heated and finally made acid with hydro-
chloric acid, a precipitate of prussian blue will be formed. The
reactions which take place are the following : —

(1) FeSOj + 2 NaOH = | Fe(OH)j + Na^SO* ;

(2) Fe(0H)4 + 2 KCN = | Fe(CN)|, + 2 KOH ;

(3) Fe(CN>, + 4 KCN = K,Fe(CN)B ;

(4) 3 K,Fe(CN)o + 4 FeCla = | Fe,[Fe(CN)e]a + 12 KCL

4. Formation of Thiocyanate. To a solution of an alkali cya-
nide add a little (NH^)gS, and evaporate the solution on a
water bath to dryness. The residue, which will now consist of
ammonium thiocyanate (NH^SCN), is treated with one or two
drops of dilute HCl, partly to insure the destruction of any
undecomposed sulphide and partly because the presence of
hydrochloric acid assists the final reaction [see reaction 5 under
Itvn (-ic)] ; if a drop of ferric chloride is now added, a blood-red
coloration will be produced because of the formation of ferric
thiocyanate [Fe(SCN)B].

If it is desired to detect hydrocyanic acid evolved from an
insoluble cyanide on treatment with hot dilute HjSO^, cover the
test tube containing the mixture with a crucible cover, on the
under side of which has been placed a drop of (NH4)jS„ and
allow the action to continue for several minutes ; then invert
the cover and dry on the water bath, and proceed as directed
above for the formation of ferric thiocyanate.

Ferrocyanides

Hydroferrocyanic acid [HjFeCCN)^] is a colorless crystalline
solid, easily soluble in water; on exposure to air the solution

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THE ACIDS 151

Isiecomes blue from decomposition. The salts of ferrocyanic
acid arc much more stable than the acid.

Solubilities. The ferrocyanides of the alkalies and alkaline
earth metals are soluble in water ; nearly all the others are in>
soluble or sparingly soluble in water and in cold dilute acids.

1. Silver Kitrate precipitates white silver ferrocyanide, insol-
uble in dilute nitric acid and in ammonium hydroxide, but soluble
in potassium cyanide solution; —

4 AgNOj + K^FeCCN), = | Ag^FeCCN), + 4 KNO^
On ignition, the precipitate is decomposed with the separa-
tion of silver and evolution of cyanogen gas: —

Ag,Fe(CN)B = |4 Ag + 1 2(CN)j + 1 FeC^ + f N^

2. Sulphuric Acid, when cold and dilute, does not decompose
ferrocyanides; on heating to boilmg, however, partial decom-
position sets in with the liberation of part of the cyanogen as
hydrocyanic acid : —

2K^Fe(CN)g + 3HjS04 =

\ KjFe[Fe(CN),] + 3 KaSO, + f 6 HCN.
Concentrated sulphuric acid, when heated, completely decom-
poses ferrocyanides with the evolution of carbon monoxide: —
K,Fe(CN)e + 6 HaSO^ + 6 Hfi =

FeSOi + 2 KjSO, -I- 3(NH,),S04 -H f 6 CO.

3. Ferric Salts, added to a slightly acid solution of a ferro-
cyanide, yield a precipitate of prussian blue.

4. The Solotios of lasoluble Fenocyanldes is accomplished by
boiling the compound with sodium hydroxide and filtering, when
the metal will be left on the filter in the form of hydroxide,
while the filtrate will contain the acid radical in the form of
sodium ferrocyanide: —

Fe^[Fe(CN),]8 + 12 NaOH - 4 Fe(0H)8 + 3 Na^FeCCN),.

The residue is dissolved in acid and the metal is tested for in
the solution obtained. The filtrate is acidified with HCl and
tested for the ferrocyanogen radical by adding ferric chloride.

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IS2 QVAUTATIVE CHEMICAL ANALYSIS

I£ the metal is one whose hydroxide is soluble in excess of
sodium hydroxide, as Zu, it may be separated from the ferro-
cyaaide by passing carbon dioxide into the alkaline solution,
boiling, and then filtering off the basic carbonate of zinc. la
the case of lead ferrocyanlde, the lead may be precipitated from
the alkaline solution by a stream of HjS.

Fusion with sodium carbonate decomposes f errocyanldes.

FBRRICYAinDES

SoinbUltles. All f erricyanides are insoluble in water and in
cold dilute adds with the exception of those of the alkalies and
alkaline earths. Heated to redness, ferricyanides decompose,
the products being iron carbide, cyanide, nitrogen, and cyano-
gen ; the last bums with a characteristic purplish flame. Sul-
phuric acid, when dilute and warm, causes partial decomposition
with the evolution of HCN. When concentrated and hot, it
effects a complete decomposition with the liberation of CO.
The equation as given by Treadwell is as follows ; —

2 KgFe(CN), + 12 HaSO^ + 12 HjO =

F'^50^\ + 3 KjSO, + 6 (NHi)|S04 + f 12 CO.

1. Silver Nitrate gives with ferricyanides a reddish brown pre-
cipitate of silver ferricyanide, insoluble in nitric acid, but solu-
ble in ammonium hydroxide and in potassium cyanide.

2. Iron Salts. Ferric salts give no precipitate, but a dark
coloration; ferrous salts give a blue precipitate of Turnbull's
blue, Fe8[Fe(CN)(]j, insoluble in acids.

3. Reducing Agents, such as HgS, SO,, and HI, readily reduce
ferricyanides to f errocyanides in alkaline solutions : —

2 KgFe(CN)jj 4- KjS = 2 K,Fe(CN)i, + {S.

Thiocyanates
Alkali thiocyanates are readily prepared by heating the cy-
anide with sulphur : —

KCN+S=KCNS;

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TBE ACIDS IS3

or 1^ heating an alkali cyanide or hydrocyanic acid with ammo-
nium polysulphide : —

KCN + (NH^S, = KCNS + (NH4),S^,.

SoloWUtles. Nearly all the thiocyanates are soluble in water
with the exception of those of silver, mercury, copper, and gold.

1. Silver Nitrate precipitates white, curdy silver thiocyaaate,
insoluble in dilute nitric acid, but soluble with difficulty in
ammonium hydroxide.

2. Ferric Salts give with alkali thiocyanate solutions a blood-
red coloration, due to the formation of ferric thiocyanate. The
color is destroyed by mercuric chloride.

Sulphides

Hydrogen sulphide is a colorless gas having a characteristic

and unmistakable odor. Its solution in water possesses a feeble

acid reaction, but it is very unstable, oxidizing readily in contact

with air with the separation of sulphur ; —

H,S + 0=.H30 + |S.

HjS reacts with bases forming hydrosulphides and sulphides,
which, if HjS is looked upon as a dibasic acid, may be regarded
as acid and normal sulphides : —

NaOH + H,S = NaSH + HaO ;
2 NaOH + HaS = NajS + 2 HgO.

Behavior on Ignition. Out of contact with the air, most
sulphides remain unchanged. The sulphides of arsenic and
mercury when heated sublime unchanged. Tin disulphide and
iron disulphide give off part of their Sulphur. AH sulphides on
being heated in contact with air (roasted) are oxidized either to
oxides or to sulphates.

Solahillties. The sulphides of the alkalies are soluble in
water ; those of the alkaline earths, aluminum and chromium,
are hydrolyzed by water with the formation of hydroxides ; all
other normal sulphides are insoluble in water.

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154 QUALITATIVE CHEMICAL ANALYSIS

1. Hydrochloric Add, when moderately strong (1:1), decom-
poses nearly all sulphides with the evolution of H,S ; the latter
may be recognized by its odor and by its property of turning
lead acetate paper black : —

ZnS + 2 Hd = ZnCI, + f HgS.

The few sulphides undecomposed by HCl are attacked by a
mixture of zinc and HCl with the liberation of HjS.

2. Silver Nitrate precipitates from solutions of sulphides or
hydrogen sulphide, black silver sulphide (AgjS), insoluble in
cold but soluble in hot dilute nitric add ; it is insoluble in
ammonium hydroxide.

3. Oxidizing Solvents, such as concentrated HNOg, a^tta regia,
HCl + KClOg, when used to dissolve a sulphide, do not liberate
hydrogen sulphide, but cause a partial separation of sulphur
and a partial oxidation of the sulphide to sulphuric acid : —

HgS+Clj=HgCla+|S;
S + 3 Cla + 4 HjO = HaSO, + 6 HCl ;
3 PbS + 8 HNOg (hot and concentrated) =

|3 PbSO;+ 1 8 NO + 4 HaO.

4. Sodium Hitroprusaide [Na/NO)Fe(CN)6] imparts to nor-
mal alkali sulphide solutions a reddish purple color. An aqueous
solution of HgS does not give this reaction.

5. Sodium Plumblte (prepared by adding caustic soda solu-
tion in excess to a lead salt) will detect a sulphide even in the
presence of free alkali or carbonate, by producing a brown or
black precipitate. This test is exceedingly sensitive.

6. For the oxidizing effect of the halogens, nitric acid, potas-
sium dichromate, potassium permanganate, ferric salts, etc., on
H^S, see page 61.

Insoluble Sulphides. Sulphides insoluble in acids, when fused
in a small nickel crucible with sodium hydroxide, are decom-
posed with the formation of sodium sulphide. If the mass is
placed on a silver coin and then moistened, a black stain of
silver sulphide (AgjS) will be produced.

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TEE ACIDS 155

Nitrites
Solutdlitles. Most nitrites are soluble in water ; silver nitrite,
however, is only sparingly soluble in water. On ignition, nitrites
undergo decomposition with the production in general of nitro-
gen oxides and the oxide of the metaL

I. Sulphuric Add, when dilute, decomposes all nitrites (dis-
tinction from nitrates) with the evolution of nitric oxide (NO) :
the latter immediately oxidizes in contact with the air to brown
nitrogen peroxide (NOj) * : —

(i) NaNO,+ HaS04=NaHS044-HNOa;

(2) 3 HNO, = HNOg -»- f 2 NO + HjO ;

(3) N0-»-0 = N03.

Nitrites are also decomposed by acetic add with gentle heat-
ing ; the NOj given off may be recognized by its turning starch-
iodide paper blue,

a. Silver Nitrate precipitates, from solutions of nitrites which
are not too dilute, white silver nitrite (AgNOj), difficultly soluble
in cold but more easily soluble in hot water.

3. Cobalt Salts solutions acidified with acetic acid give, with
moderately strong solutions of potassium nitrite, a yellow pre-
cipitate of potassium cobaltic nitrite [K8Co(NOj)s],

4- Potassitun Iodide, when added to a solution of a nitrite, and
the mixture is acidified with acetic acid, produces a separation
of iodine ; the latter may be recognized by turning starch paste
blue, or by coloring a drop of CSj or CHClg violet

5. Potassium Permanganate solution, when warmed, is bleached
by a solution of a nitrite slightly acid with dilute sulphuric
acid: —

2KMnO^-|-sHNO,-|-3HaS04 =

KjSO^ + 2 MnSOi -I- 5 HNOg + 3 H3O.

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1S6 QUAUTATIVE CHEMICAL ANALYSIS

GROUP III

The acids of this group are not precipitated by either AgNO,
or BaCi,.

Acetates

Solubilities. All normal acetates are readily soluble in water.
Some basic acetates, such as those of iron.(-ic), aluminum, and
chromium, are practically insoluble, while the normal silver and
mercurous salts are only sparingly soluble. On ignition, acetates
decompose with little or no charring and with the production of
a combustible gas.

The alkali acetates, on ignition, are converted into carbonate
and acetone : —

2 NaCaHgO, = Na,COg + f (CH,)jCO.

All other acetates tehave similarly. If the carbonate is un-
stable at the ignition temperature, the oxide is produced ; if the
latter is unstable, then the metal alone is left as a residue.

1. Sulphuric Add, whether dilute or concentrated, liberates
acetic acid from its salts ; the acid, being volatile, is easily rec-
ognized by its characteristic odor.

2. Alcohol and Conceatrated Satpharlc Add. If to a cooled
mixture of an acetate and concentrated sulphuric acid, a little
ethyl alcohol is added and then the mixture is gently heated,
ethyl acetate will be formed ; the latter is easily recognized by
its fruity odor. If amyl alcohol is used instead of ethyl acohol,
amyl acetate, having an odor resembling pear essence, will he
produced : —

CHj . COO[H -f- HO]C,H, -^ CH, ■ COOCjHs + HaO.

Acetk Kid. Etbjrl ilcoEid. Etbjrl ncMua.

The reversible reaction is made to proceed almost entirely
from left to right by the presence of the concentrated sulphuric
acid, which removes the water as soon as it is formed.

3- Silver Nitrate gives with moderately concentrated solutions
of an acetate or acetic acid a white crystalline precipitate of
alver acetate (AgCjHgO,), sparingly soluble in cold water (1.04

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THE ACIDS 1 57

parts of the salt dissolve in loo parts of water at x? C), more
readily soluble in hot water, and easily soluble in ammonium
hydroxide.

4. Ferric Chloride, when added to an alkali acetate solution,
produces a reddish brown solution, due to the formation of ferric
acetate. If this solution is largely diluted and boiled, all of the
iron will be precipitated as a basic ferric acetate : —

Fe(CH,0,)|, + H,O:?tFe(0HXC,H,O,)l + HC,H,0,.
Nitrates
Sidablllties. The nitrates, with the exception of a few basic
nitrates, such as BiONOg, are all soluble in water. Barium
nitrate, however, is only sparingly soluble in water and is almost
insoluble in moderately strong nitric acid. All nitrates on igni-
tion undergo decomposition, the alkali and alkahne earth ni-
trates yielding nitrites with the evolution of oxygen : —
KNOB = KNO, + fO.

At higher temperatures, the nitrites are decomposed with the
production of the oxides of nitrogen and a residue consisting
of the oxide or peroxide of the metal. The nitrates of the
heavy metals yield at a red heat nitrogen peroxide and oxygen.
Heated on charcoal, all normal nitrates deflagrate.

1. Concentrated Sulphuric Add, when added to a soUd nitrate,
causes the evolution of nitric acid. If the mixture is heated,
the nitric acid is decomposed with the production of brown
fumes of nitrogen peroxide (NOj): —

(i ) NaNOa + HjSO, = NaHSO* + HNOs ;
(2) 2 HNOs = fz NO, + HjO + f O.

2. Ferrous Sulphate, when added to a cool mixture of a nitrate
solution and concentrated sulphuric acid, produces a deep brown
color. The reaction may be considered as taking place in three
stages : rst, the liberation of nitric acid by the action of con-
centrated sulphuric acid on the nitrate ; 2nd, the reduction of the
free nitric acid by the ferrous sulphate, resulting in the pro-
duction of nitric oxide; and, 3rd, the solution of the nitric oxide

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IS8 QUALITATIVE CHEMICAL ANALYSIS

in the excess of unoxidized FeSOf with the formatioQ of a
brown unstable compound : —

(1) HaSO4+NaN03 = HNOB+NaHS04;

(2) 2HNO8 + 6FeS04+3H,SO4 =

3 FcjCSO^), + 4 H^O + 2 no ;

(3) 2 FeSO, + NO =(FeSOi),NO (brown compound).

This test, which is exceedingly delicate, is carried out as foU
lows : To about 3 cc. of the nitrate solution contained in a
test tube, add an equal volume of concentrated sulphuric acid,
mix, and thoroughly cool under running water. Hold the tube
in an inclined position and cautiously add a few cc. of a strong,
freshly prepared ferrous sulphate solution (free from nitrates), and
allow the tube to stand. If a nitrate is present, a brown colora-
tion will be produced in the zone of contact of the two liquids.

Nitrites give the same reaction, but may be carried out with
dilute instead qf concentrated sulphuric acid. The colored com-
pound is destroyed on warming.

3. lodlgo Solution. If to a little HCI that has been recently
boiled, a few drops of a solution of indigo in sulphuric acid are
added, and the mixture is then boiled, the blue coloration will
persist, if the HCI contains no free chlorine. If to the blue solu-
tion a nitrate in the form of a solid or in solution is added, and the
liquid is boiled, the indigo will be bleached. As thie bleaching
of the indigo is caused by the chlorine which is liberated, any
other oxidizing agent, which will yield chlorine with HCI Uke
KClOg, will produce the same result

4. C<9per Filings, when added to a nitrate, and the mixture is
heated with concentrated sulphuric acid, cause the production
of brown nitrogen peroxide fumes : —

(i) NaNOg-f-HaSO^^NaHSOj-l-HNO,;

(2) 3Cu-t-8HN0B = 3Cu(N0g),-ff2NO + 4H,O;

(3) NO + = NOj.

5. Reductioii to Ammonia. If a solution of a nitrate is made
strongly alkaline with NaOH, and a few pieces of aluminum or

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THE ACIDS 159

nnc and iron filings are added, and the mixture is heated, am-
monia gas will he evolved. Nitrites give the same reaction.

6. Free Nitric Add may be recognized even in the presence
of nitrates by adding to the solution a few quill cuttings and
evaporating to dryness on the water bath. The quills will be
found to have a yellow color, due to the formation of xantho-
proteic acid ; the same compound is formed when concentrated
nitric acid is brought in contact with the skin.

Chlorates
The chlorates are all soluble in water. On prolonged igni-
tion, they are decomposed, giving off oxygen and leaving a
residue of the chloride of the metal : —

KC108 = KCl+t3 0.
AgC10B = AgCI+f3 0.

In consequence of the readiness with which they decompose
with the Uberation of oxygen, chlorates are valuable oxidizing
agents. When they are mixed with organic matter and heated,
deflagration results.

1. Concentrated Snlpharlc Add decomposes chlorates with the
production of chlorine peroxide (ClOjX * very unstable, green-
ish yellow gas, which, on being warmed, violently explodes.
The sulphuric acid acquires at the same time a deep yellow
color, due to dissolved CIO3 : —

3 KClOu + 2 H,SOj = KClOj + 2 KHSO4 + H,0 + f 2 ClOj.

In carrying out the test, it is preferable first to warm a Uttle
concentrated sulphuric acid in a test tube and then to drop in
a vety small crystal of KCIOg. One should never look down
into a test tube, especially when performing this test Equal
conaderation is due one's neighbor.

2. Concentrated HCl, when added to a chlorate, is oxidized
with the production of chlorine and chlorine peroxide : —

KCIO, + 2 HCl - KCl-H t CH- 1 CIO, -(- H,0.

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i6o QUAUTATIVE CBEMICAL ANALYSIS

3. Aalline Sulphate. If to a solution of a chlorate in con-
centrated sulphuric acid a drop of aniline sulphate solution is
added, a deep blue coloration will be developed ; the color may
he intensified by the addition of a few drops of water. This
reaction is exceedingly delicate and may be used to distinguish
a chlorate from a nitrate.

4. Reducing Agents, as sulphurous acid or the alkali sulphites
in acid solutions, change the chlorates to chlorides : —

HCIO, + 3 HjSOj =. 3 HjSO. + HCL

ACID ANALYSIS

Preliminaty Examination

Before proceeding with the analysis for the acids, the student
should first complete his examination for metals, the results of
which will, by a proper use of the table of solubilities, restrict
the number of acids to be looked for. An example will make
this clear. If the substance under examination is soluble in
water and lead has been found, none of the acids which form
insoluble salts with lead need be looked for, viz., carbonic,
sulphuric, hydrogen sulphide, chromic, oxalic, etc. Again,
if the original substance is insoluble in water, but soluble in
hydrochloric acid, and barium has been found, one need not
look for sulphuric acid. Further, if silver has been detected
in the metallic analysis of a substance soluble in water, it is
evident that all the acids of Group II. need not be looked for.
It is also well to remember that certain acids cannot coexist
in solution, e.^., oxiding agents Uke KaCr,0„ HgAsOj, FeCl,
cannot exist with reducing agents like sulphites and iodides.
It is also desirable that the first three of the following prelimi-
nary tests be carried out before commencing the systematic
search for acids.

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PREUMINARY TESTING OF SOUDS
I. Heat a small quantity of the substance in a tube closed at
one end.

0»^*t™.

IKP.C*™«

DwmplUtion.

Naa, Pb(NO,)„ KjSO„ riuc blende.

and other substances.

Oiganic matter, tartrates, and other

odor and fbnuatioii of water.

organic acids and salts.

Water glTni oS.

Water niecfianically inclosed, water

OuMftnnot:—

of hydration, and hydroxide.

O— IdndleiaGpark;

Chlorates, peroxides, certain ozidea,

Coloriesa

nitrates, etc.

and

CO— bums with blue

Oxalates.

odorless.

flame;

tarbid.

matter.

NH,— turns red Utmus

blue;

containing N.

odor;

t^n sulphates.

Colorless

(CN)» — rect^niicd

Cyanides.

with

by odor,* and bums

odor.

with reddish flame;

MiS — reo^nized by

Mobt sulphide*.

odor;

Acetone — recc^iied

Acetates.

by odor.

NO»— reddish brown ;

Nitrates of heavy metals.

Colored

turns starch-KI

gases.

paper blue.

a, Br, I — recognized

Chlorides, bromides, and Iodides In

by color and odor.

the presence of oxidizing agents.

White.

NH, salts, HgCl, HgCI,, As,0., Sb,0»

and certain organic compounds.

Yellow.

AsiS„ HgO (accompanied by globules

ofHg).

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QUAUTATIVE CHEMICAL ANALYSIS

o^.™,

IWHCJinilH

Yellow, becoming red when

Hglr

rubbed.

Reddish brown drops, yellow

when cold.

Black accompanied by garlic odor.

As.

vapor.

Metallic globules or mirror.

Hg.

Substance chugM coto : —

Becomes black.

SaltsofCu,Ni,Co,Hii.

Salts of Fe.

Black (hot) and red (cold) ac-

Hg salts.

companied by metallic globules.

Dark red (hot), yellow (cold).

PbCrOr

Yellow (hot), white (cold).

ZnO.

2. Put a small quantity of the substance in a test tube, add a
little dilute HCl, and heat gently.

OnuVATIOH

,™„™.

co„

effervescence, turns lime water tuibid.

Carbonates.

so,

recognized by odor.

Sulphites.

so,

Thiosulphates.

H,S

. recognized by odor and by lead acetate paper.

Sulphides.

NO,

: brown, turns starch-KI paper blue.

Nitrites.

HCN : recognised by odor."

Cyanides.

3. Heat a small portion in a test tube with concentrated
sulphuric acid.

OSWBVATIOM

Add fumes are evolved which redden

Br, 1, mixed with HBr, SO^ and per-
haps HjS.

Halogen acids from their salts.
Iodides and bromides.

* Smell caDtioutl; by bnning vapor witb SmA towards m

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THE ACIDS

163

ImiCATlOK

Chlorioe — bleaching litmus.

Chloride and oxidizing agent together.

CrOjClj — (reddish brown) .

Chromate and chloride together.

aO, — yeUow color of gas and

Chlorate.

HjSO, ; gas explosive.

HF —etches glass ; yields SiF„ which

Huoride.

turns •' water bead " turbid.

HCjHjOj — recognized by odor.

Acetate.

NOj — recognized by odor and by

Nitrates, nitrites.

turning starch-KI paper blue.

SOj— recognized by odor.

Sulphite, thiosulphate, or rcdudng

agent aclmg on H,SO,.

SOj — accompanied by blackening.

Organic matter or tartrate.

CO — (without blackening) recog-

Oxalate, cyanides, ferro- and feni-

nized by burning with blue fiame.

cyanides.

COj — turns lime water turbid.

Carbonates and oxalates.

4. Heat alone on charcoal with blowpipe.

o„..™

iMDICATIOH

(u) Substance fuses and runs into charcoal.

Salts of Na, K, and Li.

{6) Substance decrepitates.

{c) Substance deflagrates.

Chlorates, nitrates.

(jd) Substance is infusible; residue mois-

tened with water reacts alkaline.

Ba, Sr, Ca, Mg.

Residue moistened with two drops

of very dilute Co(NOs), solution

and heated again gives a

blue mass.

Al.

green mass,

Zn-

pink mass.

Mg.

accompanied by garlic odor.

As.

YeUow (hot), white (cold).

Zn.

YeUowish brown (hot), white (cold).

near residue, and not volatile.

Sn.

Reddish yellow (hot), yellow (cold).

Pb.

Orange (hot), light yellow (cold).

Bi.

Reddish brown, cold ^d hot.

Cd.

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i64

QUAUTATIVE CHEMICAL ANALYSIS

5. Mix with anhydrous sodium carbonate and heat on char-
coal.

o»„.™.

I-^™-

(«) Metallic globule forais without incrustation : —

yellow.

Au.

red,

Cu.

Ag.

Pb, Sn.

brittle.

Sb, Bi.

(e) Dark and brittle magnetic mass.

Fe, Co, Ni.

6. Make borax bead test; introduce first in oxidizing and
then in reducing flame.

0.™«F^

R^a^F^

ImiciTOw

Blue.

blue.

Co.

Greenish blue.

red — opaqne.

Cu.

Green.

green.

Cr.

Yellow.

green.

Fe.

Brown.

gray — opaque.

Mi.

Violet.

colorless.

Mn.

7. Moisten substance with concentrated HCl,take up a small
portion on the loop of a platinum wire, and bold in the flame.*

OMmvAllOH

Intense yellow which perusts £3r sereral seconds.

Deep red.

Reddish yellow.

Green or greenish yellow.

Pale blue.

Ba, Cu, (K H|BO,.

* Certain snbitaacct, like the solphstet of the slkaline esithi, are not ToladUied
in the flame; in >nch caies, it is well to hold them Grtt in the ledudng Same, then
noiiten with HO, and introduce into the colorlea homcn Same.

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TBE ACIDS z6$

Method of Add Analyiis

The method employed for the detection of the acids is differ-
ent from that used in the systematic examination for metallic radi-
cals. We cannot, as was done with the metals, divide the adds
into groups by certain reagents and then separate the various
group precipitates into their componetit acids. For the most
part, the procedure consists in independently and separately
testing for each of them. From the list of adds this would
seem a long and tiresome task, but in actual practice the num-
ber of acids which must be looked for is very much reduced ;
first, from a knowledge of the solubilities and metalhc content
of the substance ; and, second, by the results furnished by the
preliminary experiments just given. The reagents BaClj and
AgNOj, when properly applied, are valuable in that they give
indications of the presence or absence of whole groups ; e.g., if to
a moderately concentrated and neutral solution of the substance,
BaClg or CaClg is added and no predpitate results, the absence of
all the members of Group I. may be inferred.* However, these
reagents cannot be used to separate the acids in the manner in
which group reagents are employed to precipitate metaUic groups.

OBHXRAL EXAMHTATIOV FOR ACIDS

Preliminary treatment of the sample with dilute HCI will dis-
close the presence or absence of the following acids : HjCOg,
HaSO^ HjSaO^ HjS, HCN, and HNO,. In the course of the
analysis for metals, HgAsOg, HjAsOj, and HjCr04 will be de-
tected. For the examination for acids, it is desirable in most
cases to have a solution which shall contain the acids in the
form of sodium salts. Such a solution, known as the " prepared
solution," may be obtained by boiling the finely powdered sub-
stance with an excess of Na^COg solution, with constant stirring,
for several minutes (i). If ammonia is given off, boil with the
addition of more Na^COg until no more of this gas is evolved,
and then filter.

* The Mlntion ihodd alto conI«in no conaidenible qiumtity of NH* utts, elM
boratei, flooride*, and tutntc* may not precipitate.

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QUAUTATIVE CHEMICAL ANALYSIS

Residtie will coo-
tais the hjdroxides,
carbonates, and basic
carbonates of the
metals (except the
alkalies, As and Sb);
it may also contaio
phosphates, flixnides,
and silicates. Re-
serve this residue,
and if these adds are
tu^ found in the fil-
trate, divide it into
two parts.

1st part. Test for
HJ-O. and SiO,.

AddifywithHNO,,
evaporate to dry-
ness, extract with
hot dU. HNO,, and
filter. Test residue
with NaPO, bead or
with HF in a plati-
num Ctudble. Test
filtrate for PO4 with
(NH4),MoO,.

zndpart. Test for

Filtrate (prepared solution) will contain the acids in
form of sodium salts -1- an excess of NaiCOi and is to
be used for the acid tests unless otherwise directed.

FrelimliuuT Tests for the Acid Gionpa
/ttil addify a small portion of the prepared solution
by the careful addition of dil. MNOi; filter if necessary
(3) and boil the filtrate until all of the COi is espelied.
Render &intly alkaline with ammonia, and boil oiF any
excess of the latter that may have been added ; filter
again if necessary. Divide this solution into 2 parts.

1st part. Test for Group I. by adding a little BaQj
and CaCli solutions (3). A white precipitate shows the
presence of the Group I. (4) ; addiiy with HQ. If
the ppt does not dissolve, HtSO» b present. If ths
group is present, test separate portions of the prepared
solutions for HjPO„ H,BO„ HF, H,C,0„ H AHiO,,
HiSiO,.

2nd part. Test for Group II. Render thesolutioa
add with HNO, and add an excess of silver nitrate.
A ppt. proves the presence of Group II. Note tlie
color of the ppt. (5) and filter.

Kesidae. Wash several
times on filter with water.
Transfer ppL to a test
tube and shake vigorously
with an excess of dilute
NHiOH. If complete
solution takes place, the
absence of HI and
H(Fe(CN)4 is shown.
HBr and HCNS may also
possibly be absent. If
Group II. is shown to
be present, test separate
portions of the prepared
solutions for HI, HBr,
Ha, HCN, H,Fe(CN)s,
H,Fe(CN)^ and HCNS.

Group HI. Test separate portions for HGO,, HNO«
and HC,H|0,.

To filtrate or solution in
which AgNOi produces no
ppt. in HNOj solution,
add more AgNO, to insure
complete precipitation ; fil-
ter if necessary, and to the
filtrate contained in a test
tube carefully add 3 to ;
drops of ammonia. Agi-
tate the upper portion of
the liquid and note the
color of any ppt. which
may form at the neutral
zone (6).

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THE ACIDS 167

ITOTBS

1. If the substance is soluble in water and contains no heavy metala, the
treatment with Na,CO, may be dispensed with. If add (preferably nitric
add) tus been used in getting the substance into solution, and the latter is
boiled, HjCO,, HjSO, H,S,0„ HjS, HCN, and HC,H,Oj will be driven off
or decomposed, and therefore should not be looked for ; the presence of all of
these acids will have been revealed, however, in the preliminary examination.
Substances insoluble in water but soluble in acids, when boiled with NajCO,
solution, may leave a residue consisting of the phosphates and fluorides of
certain metals which are not readily transposed by boiling with Na^CO,.
Substances insoluble in acids should be fiised in a platinum crucible if no
reducible metals are present, otherwise in either a nickel or a porcelain cru-
cible with Na,CO, ; the melt is then extracted with boiling water and the
solution is liltered. The filtrate will correspond to the "prepared solution "
and should be used for the acid tests. The residue is tested for phosphates
and fluorides. In certain cases where As and Sb are known to be present, it
may be necessary to remove these metals by passing HjS into the acidified
solution, filtering, and boiling out the HjS from the filtrate. The latter may
then be treated with Na^COj in the manner already described. In the absence
of nitrates and chlorates and in the presence of only metals which are pre-
cipitated by HjS, a solution for the add tests may be prepared by saturating
with H^ a suspension of about i g. of the substance in about 50 cc. of water.
Heat to boiling and filter. The filtrate after boiling to expel the H5S is used
in small portions for the acid tests. Nitrates and chlorates, if present, would
oxidize the HgS, forming HjSO,; while chlorates would be reduced to chlo'
rides, thus making the tests for these adds of no value.

2. Boiling with NajCO, will leave all of the metals in the residue, with the
eiception of the alkalies, As, Sb, and small amounts of metals slightly soluble
in excess of NagCO,. On acidifying this solution, a predpitate may be
obtained. It should be filtered off, rejected, and the filtrate again boiled to
drive out any H^S that may be liberated before neutralizing the solution with
ammonium hydroxide. All the CO^ must be expelled after addifying, other-
wise BaCO, and A^^^Og will predpitate when the group reagents are added.
Too much HNOg should be avoided, as this will form with the ammonia next
to be added an unnecessarily la^e amount of NH4NO,, in which the Ca or
Ba salts of nearly all the adds of Group I., especially the borate, fluoride, and
tartrate, are soluble.

3. CaClg b also added because the fluoride, tartrate, and oxalate of catduro
are much more insoluble than the corresponding salts of Ba.

4. If no predpitate is obtained, the absence of all the adds of Group 1. is
proved with the exception of boric acid, which is predpitated only from rather
concentrated solutions It should, however, be remembered that the presence

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i68 QVAUTATIVE CHEMICAL ANALYSIS

of much ammonium salts interferes more or less with the predpitation of aO
the adds of this group with the exception of H^O^ and H^CgOf

5. If only a doudiness is obtained with AgNO^ it indicates a trace of
dilorides which should not be reported. Ag,C,0, is difficuldy soluble in
HNO,; an excess of this add should be added before adding the AgNO, to
prevent its predpitation. The color of the silver precipitate, together with its
solubility in ammonium hydroxide, affords important indications of the add
present; Agl is yellow; Ag^, black; Ag,Fe(CN)g, reddish brown; AgCl,
AgCN, AgSCN, and AgjFe(CN)g are white; and AgBr is yellowish white.
Of these, only the sulphide, iodide, and ferrocyauide are insolubie in ammo-
nium hydroxide ; the bromide and thiocyanate are difficultly soluble in this
reagent.

6. Silver njtmte also predpitates from neutral solutions all the adds of
Group I. with the exception of HF and HjSO, ; the latter is, however, diffi-
cultly soluble in water. The color of the predpitate forming at the neutral
junction of the two liquids will often indicate which of the acids of Group I.
are present; if yellow, it may be AgiPO, or Ag,AsOj; if brownish red,
A^AsO,; if pur[^ish red, Ag,Cr04; if white, the oxalate, silicate, or borate.

SPECIAL TESTS FOR TEE ACIDS

The metallic analysis and preliminary tests completed, the
student should, with the aid of the table of solubilities, thought-
fully prepare a list of acids which are likely to be present and
hence to be looked for. No acid should be excluded which is
compatible with the solubility and metallic content of the sub-
stance. Minerals, as a rule, need not be tested for organic and
cyanogeu acids, and, if insoluble, for nitrates, chlorates, bro-
mides, and iodides. Alloys contain no acids as such ; they may,
however, contain acid-forming elements such as S, P, and Si, ■
which, by treatment with suitable oxidizing agents, will yield
the corresponding acids.

Carbonates

Treat a small portion of the finely ground substance in a
test tube with dilute HCl and warm. A carbonate, if present,
will evolve CO^ which may be recognized by its property of
rendering turbid a drop of limewater supported in a glass
tube.

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TBE ACIDS i6g

1. Sulphites, if present, would evolve SOj, which would also render lime-
water turbid. Sulphides and nitrites also liberate gases on treatment with
dilute HCI. To avoid the interference of these substances, use a strong
solution of KiCr^O^ instead of add, and waim the mixture. CO, alone will
be evolved. K^Cr^Of oxidites sulphides and sulphites, and is without action
on nitrites. The same end may be attained by treatment with acid and then
passing the evolved mixed gases through bromine water.

2. Certain carbonates are not readily decomposed by cold dilute add, e.g:,
magnesite, dolomite, and the carbonates of the heavy metals. They are all
decomposed, however, on warming the acid.

3. In making the test, care must be exercised to prevent any acid, which
may be mechanically carried up the tube in the form of spray, from coming in
contact with the drop of limewater.

4. The drop of limewater should be examined skortiy after exposure to
insure the non-formation of soluble caldum dicarbonate.

5. Where the amount of CO, liberated b small, it b necessary to heat the
add to drive out the COi, which otherwise would remain wholly in solution
and thus escape detection.

Sulphites

Treat a small quantity of the solid substance with dilute HCL
In the presence of a sulphite, SOj will be evolved; this gas
may be readily recognized by its odor and by its property of
bleaching a very dilute solution of KMn04 (see reaction 6
under Sulphites).

Thiosulphates

These are detected in the preliminary tests with dilute HCL
In the presence of a thiosulphate, SO, is evolved, accompanied
by a separation of S.

StJLPHATES

Sulphates will have been indicated in the preliminary testing
for the groups of acids. To a small portion of the " prepared
solution," add dilute HCI to acid reaction, boil to expel COa,
filter if necessary, and to the filtrate add BaClj. A white
precipitate indicates the presence of sulphates or fluosilicates.
To confirm the presence of sulphates, dry the precipitate, mix
it with a little anhydrous Na^COg, and heat on charcoal before

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I70 QVAUTATIVE CHEMICAL ANALYSIS

the blovpipe. Remove the residue from the charcoal, place it
on a bright silver coin, and add a drop of water. A black stain
confirms the presence of a sulphate.

Fluosilicates

Acidify a small portion of the prepared solution with dilute
HCl, boil out the COa, filter if necessary, and to the clear fil-
trate add BaCI, to complete precipitation. Allow to stand for
several minutes and filter. Wash and completely dry the pre-
cipitate at a low temperature. Transfer the precipitate to a
test tube, add concentrated HSSO4, heat, and hold in the escap-
ing gases a drop of water held on the loop of a platinum wire.
In the presence of a fluosilicate, the drop of water will become
turbid owing to the formation of H^SiOj. (See footnote, page
124.)

Chsohates

(a) Solutions of a dichromate or a chromate possess an
orange or yellow color which is very characteristic. Acidifica-
tion with dilute HCl, followed by treatment with H3S, will cause
a change in color to green, accompanied by a separation of S ;
hence this acid wDl be detected in the precipitation of the second
group of metals. The presence of a chromate may be detected
by acidifying the prepared solution with HNOj, thoroughly
cooling, and then adding i cc. of ether and i cc, of 3 % H3O3
and shaking. A blue color in the ether layer proves the pres-
ence of a chromate. Reaction 6, page 143.

{b) The change in color, which is an evidence of reduction,
may be brought about by a variety of reducing agents in the
presence of free acid, e.g., strong HCl and a little alcohol (see
reaction 5 under Ckromates), KI, and Na^SOg ; the last is oxi-
dized at the same time to sulphate. If the prepared solution is
colorless, chromates cannot be present.

(c) Predpitatiott Test. In the absence of sulphates, phos-
phates, oxalates, and tartrates, acidify the " prepared solution "
with acetic acid, boil to expel COj, filter if necessary, and to the
clear solution add i g. of NaCaHgOa and a little PKCaHjOa)^

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TBE ACIDS 171

solution. A yellow precipitate of PbCrOj proves the presence
of a chromate.

If the above-mentioned acids are present, acidify the prepared
solution with HNOg, boil to expel COj, filter if necessary, and
render the resulting filtrate just alkaline with ammonium hy-
droxide ; add CaClj, warm, shake vigorously, and allow to stand
half an hour and filter. The precipitate may consist of the
tartrate, oxalate, and phosphate of calcium. The filtrate may
contain sulphates besides the chromate. To remove the former,
acidify with HNOj, heat to boiling, add a slight excess of BaClg,
and filter off the BaSO^ on two folds of filter paper. To the
filtrate add several grams of NaCaHgOj to completely replace
the nitric acid by acetic acid, and heat, when a yellow precipi-
tate o£ BaCrO| will be formed.

Arsenites

Arsenites are detected in the analysis for metals. In HCl so-
lutions, HjS yields an immediate precipitate of AsjSg. Arsen-
ites are not precipitated by either magnesia mixture or ammonium
molybdate. In a strictly neutral solution, AgNOj produces ^
yellow precipitate of Ag,AsOg (phosphates respond to the s«me
test).

Arsenates

From acid -solutions, H^S slowly yit\As a yellow precipitate.
From strictly neutral solutions, AgNO, precipitates reddish
brown AggAsO^. PreaiMtates are obtained with both magnesia
mixture and ammonium molybdate. The last two tests apply
only in the absence of phosphates. For distinctions between
phosphates and arsenates, see reactions 4 and 5 under Phos-
phates. If arsenic is found in the metallic analysis, it is usually
present as arsenite or arsenate. In the absence of oxidizing
agents, as chromic and nitrous acids, arsenates are further
distinguished from arsenites, even in the presence of phos-
phates, by the ability of arsenates to liberate iodine from
KI in a solutioD acid with HCL For the detection of Iodine,
see p. 147.

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173 QVAUTATIVE CHEMICAL ANALYSIS

Phosphates

Phosphates will have been detected in a complete analysis be-
fore precipitating the third group of metals.

(a) In the absence of arsenates, a small portion of the pre-
pared solution is strongly acidified with concentrated HNOg, '
then it is evaporated nearly to diyness, diluted with water,
treated with lO cc. of ammonium molybdate soludon, and
warmed ; in the presence of a phosphate, a yellow precipitate
of (NH4)jP04 • 12 MoOg wiU be formed.

{b) Or the prepared solution is acidified with HCl, boiled to
expel CO^ filtered if necessary, made alkaline with ammonium
hydroxide, filtered again if a precipitate forms, and the clear,
cooled filtrate is treated with magnesia mixture and thoroughly
shaken. A white crystalline precipitate of NH^MgPO^ forms
in the presence of a phosphate.

1. The solution is evaporated with concentrated HNO, to oxidize any
reducing agent that may be present and which would interfere with the
(NH,)jMo04 test ; it also converts at the same time any meta- or pyrophos-
phate to the ortho form, which alone is precipitated by (NHj)^oO^.

2. If arsenic has been found, it should be removed by rendering the pre-
pared solution stroo^y acid with HCl, heating to boiling, and passing in a
stream of H,S for 30 minutes ; then filter, boil out the HjS from the iiltrate,
add HNOp and evaporate neariy to dryness; extract the residue with boiling
dilute HNO, and add to the somewhat cooled solution an excess of am-
monium molybdate. A yellow precipitate shows the presence of PO,. The
solution to be tested for PO, should not be above 70° C., as there is danger
of decomposing the reagent, with the resulting precipitation of white MoO,.

Oxalates

Oxalates should be detected before proceeding with the pre-
cipitation of Group III.

Slightly acidify some of the prepared solution with acetic acid,
boil out the COj, and filter if necessary ; warm the filtrate and
add an equal volume of a saturated CaSO^ solution. A white
crystalline precipitate indicates the presence of an oxalate.

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TBE ACIDS 173

Confirm by filtering ofiF the precipitate, washing it with water,
dissolving it in hot dilute HgSO^, and adding a drop of dilute
KMnOf solution. In the presence of an oxalate, the KMnOj
will be bleached. (See reaction 4 under Oxalates.)

nOTES

The solution is rendered add with acetic add to prevent the predpitation
of carbonates and phosphates. CaF, may be predpitated, but may usually be
distinguiahed from CaC,0^ by the &ct that the former is gelatinous while tlie
latter is crystalliae. It is, however, better to make the confinnatoiy test

Fluorides

I. The etching test (see page 133) is not applicable in the
presence of silicates or silica.

3. The test depending upon the formation at SiF^ and the
detection of the latter by its property of rendering a water
"bead," held on the loop of a platinum wire, turbid (see
page 132), is applicable to fluorides in the presence of SiOg or
silicates. To insure a positive test, a little sand .or dry sodium
silicate should be added.

3. Silicates which are not decomposed by concentrated HgSOf
may be tested for fluorides by fusing with 6 to 8 times their
weight of a mixture of equal parts of sodium carbonate and po-
tassium carbonate, extracting the melt with water, and filtering.
The filtrate' will contain all of the F as NaF, as well as the silica
in the form of NajSiOg. Acidify with acetic acid and filter
off any precipitate which forms. To the filtrate, add CaClg and
allow the mixture to stand for some time. Collect the precipi-
tate on a filter, dry, and apply the tests for a fluorida

Borates
I. Tnrmeric Pa^er Test Dip a piece of turmeric paper into
a small portion of the original or prepared solution acidified
with HCl and dry it; this may be conveniently accomplished
by placing it on the outside of a test tube containing water
which has just been heated to boiling. In the presence of a

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174 QVAUTATIVE CBEUJCAL ANALYSIS

borate, the turmeric paper assumes a permanent reddish brown
color, which, on treatment with a drop of caustic alkali, i&
changed to a greenish black color.

2. The Flame Test (see reactions 6 and 7 under BoraUs)
may be conducted on a portion of the original substance, pro-
vided Ba and Cu are both absent If these metals are present,
the test may be applied by first removing the Cu with HjS and
then the Ba with sulphuric acid. If the test is carried out in a
test tube provided with a stopper, through which passes a glass
tube drawn out near the end, and the mixture is heated, only
the vapors of boron ester will escape. If the issuing gas is
lighted, it will burn with a green flame. The advantage of this
form of apparatus is that, as neither Ba nor Cu form volatile
compounds under these conditions, they do not interfere.

BOTES tm TEE TDimBIC TEST

Oxidizing agents like chlorates, chrotnates, and iodides interfere with this

test by destroying the turmeric. HNO, is an exception. Chlorates and

chromates may both be reduced by treating the original substance contained
in an evaporating dish with solid Na^SOj, adding dilute HG, and warming
after the reaction has proceeded for some time, to drive out the excess of SOj.
Filter, if necessary, and boil the filtrate with a slight excess of NajCO, ; dilute,
and filter. Iodides, if present, may be removed by precipitation with AgNOj
after rendering the solution acid with HNOj. FeCl„ if present, will color the
turmeric paper brown on concentration, but will give a brown instead of a
greenish black color when the dried paper is treated with caustic soda. It is
evident that if the prepared solution is used, Fe cannot be present.

Silicates

1. The NaPOgbead test may be applied to the original sub-
stance.

2. Evolution of SIF4. In a platinum crucible, treat a mixture
of equal parts of the dry substance and CaFj (free from SiO,)
with a little concentrated HjSOj, and heat under a hood. A
drop of water, held on the loop of a platinum wire, when
brought near the mouth of the crucible, will be rendered turbid
by the escaping SiFj. About 2 cc. of aque<His HF may be
used instead of the CaFj.

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THE ACIDS

Tartrates

The presence of tartrates will be indicated when the substance
under examination is heated in a closed tube, as well as by the
characteristic behavior when heated with concentrated HjSO^
(see reaction i under Tartrates).

1. Concentrate the prepared solution to about 0.5 cc, just
acidify with acetic acid, and add 2 cc. of KCjHjOj ; shake vigor-
ously and allow the mixture to stand. A white crystalline pre-
cipitate may be KHC4H,0a. Confirm by dissolving in a few
drops of dilute KOH solution, and precipitate the tartrate with
a little AgNOjj dissolve the precipitate in a slight excess of
ammonium hydroxide and carry out the silver mirror test as
described in reaction 2 under Tartrates,

2. If no heavy metals are present and the substance is soluble
in water, the silver mirror test may at once be applied.

3. If heavy metals are present, dissolve the original substance
in water or in the least possible amount of dilute HCl, Remove
the metals of Groups I. and II., if present, by means of H^S;
and those of Group III. with NH^OH and (NH^^S (Al and
Cr will, of course, not be precipitated). The clear filtrate is
acidified with HCl, boiled to expel HjS, and is finally rendered
alkaline with NH4OH. An excess of CaClj is then added and
the mixture is shaken vigorously, allowed to stand for a short
time, and finally filtered. The precipitate, which may consist
of CaC^H^Oa, CaCaO^, and Ca/PO.V is treated with a cold,
strong NaOH solution to dissolve out the CaCjH^Og, then it is
stirred thoroughly, diluted, and filtered. If a precipitate forms
on heating the clear filtrate to boiling, a tartrate is indicated.
Confirm by filtering while hot, wash the precipitate, and transfer
it to a test tube. Add i drop of NH^OH and a little AgNOs,
and warm. In the presence of a tartrate, a black precipitate or
a silver mirror will be formed.

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176 QUAUTATIVE CBEMICAL ANALYSIS

Iodides

I. Iodides, if present, will be detected in the preliminaiy ex-
amination of the substance with concentrated H,SO^.

3. To a portion of the original or prepared solution acidified
with HCl, add a little potasBium nitrite solution or chlorine
water and then about i cc. of CS, or CHCls, and shake vigor-
ously. An iodide, if present, will color the CSj or CHCls violet.

3. AgNO, in HNO3 solution precipitates yellow Agl, prac-
tically insoluble in NH^H.

nOTBS

Nitrous add — (.«., a nitrite in add solution — is preferable to dilorine as
an iodine liberator for the reason that an excess of the former does not hinder
the reaction (see reaction 4 under fodides). The liberated iodine may also
be recc^imzed by the blue compound it forms with starch paste. Insoluble
iodidea are tested for the halogen by one of the methods given under " iHiolu-
bU Substances," page 195.

Brouiijes

1. Bromides, if present, will be detected in the preliminary
examination of the substance with concentrated HgSO^.

2. To a portion of the original or prepared solution, add with
HCl, add I cc. of CS, or CHClg. Cautiously treat with small
amounts of CI water and shake vigorously after each addition.
In the presence of bromides, the CHClg or the CSg will acquire
a reddish or yellow color, depending upon the amount of bro-
mide present (see reaction 2 under Bromides).

Iodides, if present, intofeie with the test by imparting a violet color to the
CHCI, or CSr If the amount of iodide present is large, chlorine wato* should
be added until an intense violet color is produced in the CHCI, or CS,; the
liquid is then carefully decanted or the aqueous portion is removed to another
test tube by means of a pipette, and there treated with fresh portions of CS^.
and CI water. If the CS, is still colored a deep violet, the operation is re-
pealed until only a ^nt pink color is imparted to the CS,; now, on adding a
little more CI water and shaking, a brown or reddish color will be produced If

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TEE ACIDS 177

a bromide is preaent. If the amount of iodide in the original solution is
small, as is shown by the bint purple color of the CS^ more chlorine water
should be added, without decanting the liquid, and the mixture should be
shaken after each small addition ; in the presence of a bromide, a character-
btic brown color will fimdly be observed in the CS, layer. Chlorine water
exercises a selective action, liberating practically all the iodine first ; an excess
will oxidize the latter to colorless iodic add; and on further addition of
chlorine water, bromine will be liberated. Insoluble bromides are treated as
directed wiAa " /moluMe Substances,^ p3ge 195-

Thiocyanates, cyanides and ferrocyanides interfere with the detection of
bromides by the chlorine water test for the reason that these adds are readily
oxidized by the reagent added to liberate the Br. This difficulty may be
overcome by the method devised by Curtman and Wickoff which is based on
the fa.Qt that in a solution slighdy add with H,SO,, cuprous sulphate (pre-
pared by adding H^O, to CuSO,) predpitales cyanides, ferrocyanides, and
thiocyanates (also iodides), leaving in solution bromides and chlorides.

Method. The solution to be tested, which should be neutral or slightiy acid
with H^0„ is treated with 1 5 cc. saturated solution of SO,. Heat to boiling
and while hot add slowly 2 N — CuSO, until an excess is added- The solu-
tion should be blue ; a green color shows insuffident CuSO,. Filter while hot
and wash the ppt. twice with hot water, adding the washings to the filtrate.
Boil down the filtrate to 5-10 cc. to concentrate the solution and to expd the
excess SO,. (A slight white ppt. which may separate should be discarded.)
Transfer solution to a test tube and cool. Now add t cc. 3 M - H,SO, and i
cc. I fa KMnO, and shate. Add 0.5 cc- CS, and shake again. A yellow
color in the CS, layer proves the presence of Br. The add and KMnO, are
added and shaken first in order that the CS) may not be in contact with the
KMnO, longer than is necessary, since they react with the formation of a littie
MnOj which with vigorous shaking may dissolve in the CS^ yielding a color
indistinguishable fi^m that given by small amounts of Br.

Chlorides

In the abseoce of bromides, iodides, cyanides, ferrocyanides,
and thiocyanates, a white precipitate, obtained with AgNOg
in a solution acid with HNO^ is proof of the presence of
chlorides.

Chlorides In the presence of iodides and absence of bromides,
cyanides, and ferrlcyanldea are tested as follows : To the HNO,
solution, add AgNOg to complete precipitation, filter, and wash;
digest the precipitate for several minutes with cold ammonium
hydroxide and filter ; finally acidify the filtrate with HNOg, when

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178 QUAUTATIVE CHEMICAL ANALYSIS

the formation of a white curdy precipitate shows the presence
of a chloride.

Chlorides In tlie preseace of Bromides and Iodides may be
detected by one of three following methods : —

1. The Cliromyl Chloride Method. In a small, dry distilling
Sask, place a mixture of some of the powdered original sub-
stance, or the residue obtained by the evaporation to dryness
of a portion of the prepared solution, and powdered KjCraO, ;
add s cc. of concentrated HaSOj, and heat. Absorb any fumes
that may be evolved in dilute NH^OH. The latter will be
colored yellow if a chloride was originally present (see reaction
4 under Chlorides).

2. Hart's Method. Principle: HI is oxidized by a ferric salt
and the I set free is boiled off; HBr is then oxidized with
KMn04 and the liberated Br is removed by boiling ; any resid-
ual substance which will give with AgNOj a white precipitate
insoluble in HNO3 and soluble in ammonium hydroxide, must
be a chloride. The method is not reliable for the detection of
very small amounts of chlorides in the presence of relatively
large amounts of the others.

Method. The solution coDtained in an evaporating dish is rendered

sliglitly acid with dilute HjSOf, then treated with 3, concentrated solution of
ferric alum, and the mixture boiled until no more iodine is given off. This
point may be determined by holding in the escaping vapors a piece of paper
moistened with starch paste, which, in the presence of iodine, will be colored
blue. When the expulsion of the iodine is complete, KMnO, solution is
added in a quantity sufficient to give the solution a purple color which does
not disappear on boiling. The KMn04 oxidizes the HBr, setting bromine
free, and this halogen escapes with the steam. The boiling is continued until
a piece of moistened starch-iodide paper, he^d in the vapor, is no longer
turned blue, showing the absence of bromine. If the solution is now purple,
showing an excess of KMoO,, a few drops of alcohol are added, the mixture
is boiled with stirring, and the brown hydrated MnO, is filtered off. The fil-
trate, which should be colorless, is treated with a few drops of AgNOg. A
white precipitate, insoluble in HNO, and soluble in ammonium hydroxide
proves the presence of a chloride.

3. Vortmann's Method consists in acidifying the prepared
solution with acetic acid, adding PbOj, and boiling until no more

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THE ACIDS 179

bromine and iodine are given off (as shown by tests) and Ibe
solution on settling is colorless.

All the hydrobromic acid and part of the bydriodic acid are
oxidized by the PbO,; the remainder of the iodine, combined in
the form of lead iodide, settles on the bottom of the beaker
along with the excess of PbO, added. Filter and wash the
precipitate with hot water, and test the filtrate for chlorides
with AgNOg.

ROTES

Cyanides, ferrocyanides, ferricyanidea, and thioqranates interfere wilii the
tests for the halides ; they must therefore be removed before the tests are
applied. This is accomplished by completely predpitating both cyanides
and halides nith AgNO„ then filtering, drying, separating the precipitate from
the filter, and igniting in a dish or crndble. By this procedure, the cyanogen
compounds are decomposed with the separation of Ag, while the silver halides
remain unchanged. The latter are best got into solution by fusing them with
Na^CO,, extracting the melt with water, and filtering. The filtrate will con-
t^ NaCl, NaBr, Nal, and an excess of Na,CO,. The solution is acidified
with HNOg and the tests for the halogen adds are made as given above. Or
the residual silver halides may be treated with Zn and dilute sulphuric add,
and the acdoa allowed to continue for half au hour. The halogens go into
solution as Zn salts, and, after filtering, the filtrate is tested for the halogen
adds as given above.

Ferrocyanides

A small portion of the prepared solution is acidiiied with
HCI and a little FeCl, is then added. In the presence of a
ferrocyanide, a blue precipitate of prussian blue is obtained.

Fesricyanides

1. To a small portion of the prepared solution acidified with
HCI, add a freshly prep^ed solution of FeSOj ; the formation
of a dark blue precipitate of TumbuH'sblue proves the presence
of a fenicyanide.

2. From a nitric acid solution, AgNOg precipitates reddish
brown AggFe(CN)ft.

Thiocyanates

I. Acidify a portion of the prepared solution with HCI and

add FeClg! a deep red coloration, due to the formation of

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i8o QUALITATIVE CHEMICAL ANALYSIS

ferric thiocyanate, proves the presence of a thiocyanate. The
solution is acidified with HCl to prevent the interference of
(i) acetic acid, which, with FeClg, would give a red coloration
owing to the formation of ferric acetate; and (2) to prevent
tartaric acid and other hydroxy- acids from combining with
FeCIa.

irOTES

Ferri- and feiro-cyanides interfere by yieldiag precipitates or blue solutions
which may completely mask the red color due to HCNS. Iodine, set free by
oxidizing agents which may be present, also interferes with this test by the
color it imparts to the solution. All these interfering substances may be
removed by distilling the HCNS. This is accomplished by adding to a por-
tion of the prepared solution acidified with HCl a little SnCl, sufficient in
amount to reduce any I or Br present to their corresponding halogen acids,
boiling, and then absorbing the HCNS, which distills over, in a test tube con-
taining FeClj, when characterbtic red Fe(CNS)a will be formed.

Cyanides

1. Cyanides will have been detected by the odor of HCN in
the preliminary examination with HCl and concentrated HjSOj.

2, To a portion of the prepared solution, add 2 cc. of NaOH
solution, and treat with a little FeSO^ and a few drops of
FeCls; heat gently for a short time and then acidify with HCl.
A blue precipitate of Fe4[Fe(CN)g]g proves the presence of a
cyanide (see reaction 3 under Cyanides).

BOTES

The presence of a ferricyanide, ferrocyanide, or thiocyanate interferes with
test z. When these are present, proceed as follows ; Put into a small distill-
ing flask about 15 cc. of water that has been saturated with CO,, add an
excess of solid NaHCOg, and finally some of the powdered original substance.
Quickly stopper the flask and distill under ahmd, catching the distillate in
a little NaOH solution, and apply test 2. TFe HCN contained in the dis-
tillate is derived only fivm the simple cyanide by the action of the relatively
stronger carbonic acid.

The method of Bamebey may abo be employed to advantage. This test
depends upon the fact that alkali cyanide solutions have a solvent action on
CuS. Render 10 cc. — CuSO, alkaline with NH^OH and treat with a few
bubbles of H,S. Divide the suspension of CuS thus formed into 2 portions ;
and to one add a little of the prepared solution and shake. Compare the

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TBZ ACIDS i8i

ttibes. A bleacfaii^ of the color in the treated tube shows the presence of a.
cyanide.

SuLPHroES

1. Most sulphides will have been detected in the preliminary
treatment with dilute HCI by the evolution of HjS, which may
be recognized by its odor and by its property of turning lead
acetate paper black.

2. If ayua regia or strong HNOg is used to get a sulphide
into solution, the latter will be oxidized to sulphate with more
or less separation of sulphur.

3. If treatment with HCI does not effect the decomposition
of a sulphide, add Zn and dilute HjSOj to the substance con-
tained in a test tube, loosely stoppered with a cork covered with
filter paper moistened with lead acetate, and allow the mixture
to stand for some time. Sulphides which do not respond to
test I are usually decomposed by this treatment, yielding H^S,
which will blacken the lead acetate paper.

4. Sulphides unattacked by acids should be fused with a little
NaOH on a porcelain crucible cover ; if the melt is placed on
a bright silver coin and moistened with a drop of water, a black
stain due to AgjS will form.

It must be remembeTe<f, however, that sulphates in the pres-
ence of organic matter may be reduced to sulphides when fused
with NaOH, and thus give the final test

. J. GROUP III
jBf?'^™ -' Nitrates

I. Acidify a portion oPthe prepared solution or the concen-
trated water extract of the original substance with dilute HaSOj,
then add an equal volume of concentrated HJSO4, and cool
thoroughly in a stream of running water. Incline the tube and
i carefully add 2 to 3 cc. of a strong freshly prepared FeSO^ solu-
I tion, and allow the mixture to stand. In the presence of a
I nitrate, a brown coloration will form at the junction of the two
I liquids.

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QUAUTATIVE CHEMICAL ANALYSIS

Chromates, iodides, broTiudes, chlorates, fenicyanides, feirocjramdea, and
permaogaiuites interfere with the test. Nitrites give the same reaction (see
reaction 2). Iodides and bromides in contact with concentrated HeS04 are
parUatly oxidized with the liberation of free I and Br ; these, by coloring the
solution, interfere with the test. The halides may be removed by precipita-
tion with AgiSOt (free from nitrates). Chromates will be reduced by FeSOj,
yielding green Cr2(S04)j, which will obscure the brown color. Permanganates
by their strong purple color will mask the reactioD. Both chromates and per-
manganates may be removed by adding solid NagSO, and dilute H2S04, boil-
ing until the solution is gi'een, and then precipitating the Cr and Mn salts
with an excess of NaiCO.. Filter, addify the filtrate with dUute HjSOi, and
make the test on the resulting solution. Chlorates interfere on account of
ClOi, which will form on adding concentrated HaSOt; these will also be
reduced by the above treatment. Ferro- and ferri-cyanides yield with FeSOt
blue precipitates, and hence interfere with the reaction. These may be re-
moved by the addition of ferrous and ferric salts and a little dilute H^SO^
heating the mixture to boiling, and adding BaQj to precipitate the HiS04-
The H1SO4 and BaOj are added to form heavy BaSO«, which will have the
effect of carrying down the blue precipitates, which are difficult to filter when
alone. Altliough provision is made for the removal of interfering elements,
these are of rare occurrence in mixtures ordinarily met with. The coloration
test is therefore the one most frequently employed for the detection of the
nitrates.

2. Reduction to Ammonia. Render either the aqueous extract
of the onginal substance or the prepared solution strongly alka-
line with NaOH, and boil with stirring until no more ammonia
is given off. Add some aluminum turnings, or a mixture of
granulated zinc and iron filings, and heat again. In the presence
of a nitrate or nitrite, the odor of ammonia will be evident (see
reaction 5 under Nitrates).

Nitrites

1. Nitrites will have been detected in the preliminary exami-
nation with dilute HCl; the NOj fumes given off may be readily
detected by their property of turnuig starch-iodide paper blue,

2. Brown Coloration Test. The same as with nitrates except
that in this case acetic acid or dilute HSSO4 may be used instead
of concentrated H35O4.

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TEE ACIDS 183

Acetates

1. Acetates are detected in the preKmmary treatment of the
original substance with concentrated HgS04 by the odor of
vinegar.

2. Treat some of the original solid substance contained in a
small evaporating dish or beaker with l to 2 cc. of amyl alcohol
and s cc. of concentrated HJSO4, and heat gently. The char-
acteristic odor of amyl acetate ("pear essence") indicates the
presence of an acetate. If ethyl alcohol is used, the odor of
ethyl acetate will be made evident on warming) the mixture (see
reaction 2 under Acetates).

Chlorates
I. Chlorates are recognized by their behavior when treated
with concentrated H^SO^. Heat about i cc. of concentrated
HjSOj in a test tube, remove from the flame, and under a hood
{pointing moutk of tube toward back of hood')zAt, a very minute
amount of the original substance. In the presence of a chlorate,
greenish yellow ClOj will be evolved ; the evolution is accom-
panied by a slight explosion if the gas is sufficiently heated.

3. In the absence of halogen acids, a small portion of the
solid substance is ignited in a small porcelain dish at a tempera-
ture just below a red heat; it is then cooled, extracted with
water, transferred to a test tube, and finally treated with a few
drops of silver nitrate. A white curdy precipitate of AgCl
proves the presence of a chlorate.

3. If halogen acids are present, they must be removed by
adding to the boiling solution acidified with HNOg an excess of
AgNOg and filtering. To the filtrate, the volume of which
should be 50 cc, add 5 cc. cone. HNOg and 5 cc. saturated SO,
solution. Heat A white precipitate of AgCl proves the pres-
ence of a chlorate. (See reaction 4 under Chlorates.')

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PART III

ANALYSIS OF GROUP UV (METALS) IN
THE PRESENCE OF ORGANIC MATTER,
PHOSPHATES, OXALATES, ETC

The phosphates, fluorides, oxalates, borates, and silicates of
the metals of Groups III. and IV., including Mg, are soluble in
mineral acids, but are precipitated when the free acid which
holds them in solution is neutralized by ammonium hydroxide.
Should any of these acids be present in the original solution,
they will offer no difficulties in the analysis of Groups I. and II,,
for in these the solution is kept acid. On proceeding, however,
to precipitate Group III. the solution is first rendered alkaline,
and, as a consequence, there will be precipitated along with the
metals of Group III, part or all of the metals of Group IV. as
phosphates, oxalates, etc., depending upon the quantity of these
acid radicals present. It is evident, therefore, that a different
procedure from that given must be followed for the analysis of
Group III. if these acids are present.

It will be recalled that certain non-volatile organic acids and
compounds, as tartaric acid, citric acid, sugar, and starch, hinder
the precipitation of the trivalent elements Al, Cr, and Fe(-ic) as
hydroxides and basic acetates. For this reason, before proceed-
ing with the Third Group analysts, it is necessary to test for non-
volatile, organic matter, and, if found, to remove it The
presence of organic matter will have been indicated on heating
a small portion of the original substance in a tube closed at one
end. Blackening of the residue, accompanied by a burnt odor,
indicates the presence of organic matter. If the substance
under examinatioa is a solution, evaporate a small portion to

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i86 QVAUTATIVE CHEMICAL ANALYSIS

dryness, heat to a dull red heat, and look for indications of
organic matter.

Test for an Oxalate. To a small portion of the filtrate from
Group II., from which the H^S has heen expelled, add an ex-
cess of Na^COg, boil vigorously for a moment, and filter. Render
the filtrate slightly acid with acetic acid, boil oflf the CO,, and
then add an equal volume of a saturated CaS04 solution ; a white
crystalline precipitate proves the presence of an oxalate.

Organic, matter and oxalates may both be removed by the
following procedure ; To the residue obtained by evaporating
the filtrate from Group II. to dryness, add S cc. cone. HjSO^ and
heat gently until the mass has completely charred. Cool. Add
5 cc. cone. HNO3 and heat (gently at first) until fumes of SOg
are given off. Cool. Add 5 cc. more cone. HNOg and evapo-
rate again to SOj fumes. Repeat this treatment with HNO3
and evaporating to SOg fumes until the solution is either color-
less or possesses only a faint straw color. (Three treatments
are generally sufficient.) Cool. Cautiously dilute with 25 cc.
water, boil to expel gases and filter using a double filter.
Analyze the filtrate for Groups III. and V. and for Ca, if the
latter is not found in the residue. The residue may consist of
BaSO^, SrSO,, CaSO, and anhydrous Crj(SO,V Boil the
residue for 10 minutes with 20 cc. of a saturated Na^CO, solu-
tion and filter. Wash the residue until the washings after
being acidified with HCl, fail to give a test for sulphates.
Reject filtrate and washings. Heat residue with 15 cc. diL
HNOg and filter. Analyze filtrate for Cr, Ba, Sr, and Ca.

Test for Phosphates. To about 2 cc. of the filtrate from
Group II., from which the H^S has been removed, add a few
drops of concentrated HNOg and evaporate nearly to dryness ;
take up with a little dilute HNOj, transfer to a test tube, add an
equal volume of ammonium molybdate solution, and heat gently
{do not boil). A yellow precipitate of (NH4)8P04 • 12 MoO,
proves the presence of a phosphate.

Silicates, if present, should have been detected in the prelim-
inary examination of the solid substance with a NaPOg bead ; and
should have been removed, preferably before proceeding with

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PHOSPHATE SEPARATION 187

the metallic analysis, by evaporating the solution add with HCl
or HNOg* to dryness, desiccating at 120°, extracting the residue
with a few cc. of concentrated HCl,* diluting, heating, and filter-
ing off the dehydrated and insoluble silica. The latter may then
be verified by the NaPOg head test, or by treatment in a plati-
num crucible with CaFj and concentrated HjSO^, heating, and
testing the escaping vapor with a drop of water (see reaction I,
page 132).

If, however, the analysis has befcn begun without regard to
the presence of silicates, the filtrate from Group II, should be
tested for this acid radical, and, if found, removed by the pro-
cedure just outlined, before proceeding to precipitate Group III.

Borates and fluorides are usually held in solution by the
NHjCl present, and hence in their presence no modification
of the usual scheme need be made.

Outline of Method to be Used In the Presence of Phosphates
Oxalates, silicates, fiuorides, borates, and non-volatile organic
matter having been disposed of, it only remains to provide a
method of analysis for the Third Group metals which shall
include the presence of phosphates. The scheme which follows
is based upon the fact that of the phosphates of Groups III.
and IV,, only those of Al, Cr, and Fe (-ic) are insoluble in acetic
acid; if, therefore, the iron is oxidized and the free HCl is
replaced by acetic acid, part or all of the trivalent metals pres-
ent will be precipitated as phosphates, depending upon the
quantity of phosphoric acid present. If the amount of FO^ is
less than that required to combine with all of the Fe(-ic), Al,
and Cr, the precipitate which forms will contain all the PO^.
If, on the other hand, the quantity of PO4 present exceeds that
required to unite with the trivalent metals, it will be evident that
more trivalent metals will have to be added to completely pre-
cipitate the PO4. The metallic radical used for this purpose is
Fe(-ic), partly because its phosphate is the least soluble in acetic
acid, but chiefly because it is possible, when a salt of ferric iron
is used, to tell when all the phosphate has been precipitated ; for
' If meUli of the fint group txe pietent, ute HNO( instead of HO.

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i88 qUAUTATlVE^ CHEMICAL ANALYSIS

when this condition is reached, any excess of ferric salt added
will yield with the acetate radical present red ferric acetate,
which can readily be recognized by its color. Now, on adding
an excess of NaCgHgOj, largely diluting, boiling the solution,
and rapidly filtering, the separation of all of the trivalent metals,
including the excess of iron added, together with all the phos-
phoric acid, is accomplished (see reactions 6 and 7 under /ro»,
pages 83 and 84). The filtrate, now free from PO^, is concen-
trated by evaporation, and then treated for the remaining metals
of Groups III. and IV. in the usual way.

The Phosphate Sepoiatloii

If phosphates are shown to be present, the entire filtrate from
Group II. is boiled until all of the H3S is expelled, a few drops
of concentrated HNOs are then added, and the solution boiled
for several minutes to insure the complete oxidation of the
iron present. Test a separate small portion, about 2 cc,
for iron by adding a few drops of KjFe{CN)((. A blue pre-
cipitate proves the presence of iron. The remainder of the
solution is transferred to a beaker of 500 cc. capacity and is
treated with ammonium hydroxide, added drop by drop with
vigorous stirring, until a sl^ht precipitate is produced which
persists after stirring for 3 minutes. Now add caatiausly, with
constant stirring, dilute HCl, drop by drop, until a clear solu-
tion is obtained; then add 8 g. of NH^CjHgOj and 8 cc. of
50 per cent, acetic acid. If the solution is not red, add FeClj
solution drop by drop,with stirring, until the solution assumes a
deep red color, avoiding an excess. In the presence of a pre-
cipitate, the color of the solution may be seen by filtering a
small portion ; the filtrate should give, when made alkaline with
NH^OH, a reddish brown precipitate of Fe(OH)g, showing that
an excess of Fe (-ic) is present ; if a light-colored precipitate is
obtained with NH^OH, more FeClg should be added. Now dilute
the solution with hot water to 400 cc, heat rapidly to boiling,
and boil for 3 minutes only. Allow the precipitate to settle,
filter on a large fluted filter contained in a 10 cm. funnel, and wash

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PREPARATION OF THE SOLUTION 189

with hot water. The residue may consist of the phosphates
and basic acetates of Al, Cr, and Fe(-ic), and it may also con-
tain small amounts of Ni, Mn, and Zn. The filtrate, which
should not have a yellow color, is at once evaporated in a large
evaporating dish to 50 cc, and any precipitate which separates
out is filtered off and rejected. The filtrate, now concentrated
and free from PO4, is analyzed as usual for Groups III,, IV.,
and V. ; the tests for Al, Cr, and Fe should be omitted, as these
metals will be in the residue from the basic acetate separation.
The precipitate, consisting of the phosphates and basic acetates
of Al, Cr, and Fe (-ic), is transferred to a beaker with the aid
of 20 cc. of water, 2 g. Na^Oj are added, the mixture is boiled,
with stirring, and finally filtered. The residue, consisting of
Fe(OH)s, is rejected. The filtrate may contain NajAlOj,
Na^CrOj, NagPO^, and an excess of NaOH. If the solution is
yellow, chromium is present; if colorless, Cr is absent Alumi-
num is detected by acidifying the solution with HNOg and then
rendering alkaline with ammonium hydroxide; the white gelati-
nous precipitate of AlPO^ or Al(OHg) is filtered off, washed
with hot water several times, and the presence of aluminum is
confirmed by igniting with a few drops of Co(NOg)3 in the
usual way. The filtrate will contain the chromium as NagCrO^.

PREPARATION OF THE SOLUTION

The preliminary tests completed, the next step in the system-
atic examination is to get the substance into solution. This
is accomplished by the use of the solvents, water, nitric acid,
hydrochloric acid, and agt^ regia. In determining the solvent,
it is advisable to experiment with small portions of the original
substance at first, finally treating, after the proper solvent has
been found, about one gram of the original material for the
analysis. With mixtures, more than one solvent may be re-
quired. In such a case, it is a good plan to keep, and analyze
separately, portions dissolved by different solvents; the addi-
tional labor involved will be compensated by the information

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I90 QUAUTATI7E CBBMICAL ANALYSIS

which this procedure will supply conceming the manner in
which the metallic and acid radicals are united.

Treatment with Water
Treat a small quantity of the finely powdered substance with
about 25 cc. of water and heat to boiling. If solution takes
place, treat one gram of the sample in the same way and analyze
the resulting solution for the metals and acids. Test the aque-
ous solution with litmus; if alkaline, the presence of a car-
bonate, hydroxide, sulphide, phosphate, borate, or cyanide is
indicated ; if acid, it may point to an acid salt, free acid, or the
salt of a heavy metal. If no solution appears to have taken
place, filter, and evaporate some of the clear filtrate on a watch
glass to dryness; if only a slight residue remains, the substance
may be considered insoluble in water; if a moderate amount of
residue Is left, it indicates that the mixture contains a water-
soluble component. In that case, treat a gram sample with
boiling water and filter. Analyze the aqueous extracts for acids-
and bases. Treat the residue with acids as given below.

ROTES
If iodides or bromides, particulaily the fbnner, have beea indicated in the-
preliminary test with cone. HgSO^ the original substance, whether it dissolves
wholly or in part in water, must be treated for the removal of these faalldes
before the analysis for the metals is begun. This is accomplished by treating
the substance with HNO, and heating until no more I is evolved. If iodides,
are not removed, there will be danger of forming txpiosive brownish black
nitrogen iodide, 10 making the preliminary test for Group III., because of the
actioa of iodine set free by the treatment with HNOj, on the ammonia which
Si next added.

Treatment with Adds
If the substance is insoluble in water, treat it or the residue
from the water treatment successively with hot dilute HCl and
hot concentrated HCL If these fail to effect solution, try the
action of dilute and concentrated HNOg on separate small por-
tions; if these also fail, add HCl to the mixture containing
HNOg, thus forming aqua regia, and beat. If still insoluble,,

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PREPARATION OP TUB SOLUTION 191

examine it by the method given for "InsolubU Substances,"
page 197.

BOTES

1. During the treatment with HCl, indicatioDS of the presence of certain
acids will be given (see "* PreUtKinary Examination^'' page 163).

2. If Hg and As are present, boiling with HCl may cause these elements
to be lost by volatilization \ the remedy is to be sought in the use of HNO„
which oxidizes them into compounds which aie not readily volatile.

3. If complete solution with HQ is obtained, the absence of Ag, Hg (-ous),
and large amounts of Pb b indicated. Evaporate the solution nearly to dry-
ness to expel most of the add, dilute, and analyze the resulting solution,
beginning with Scheme II.

4. Treatment with concentrated HCl may cause the precipitation of Pb in
the form of crystalline needles of PbCI, ; when this is the case, filter them olF,

dissolve in boiling water, and test for Pb.

5. If the HG treatment causes gelatinous silicic add to separate, evapo-
rate the mixture on the water bath to dryness, dehydrate by heating to 120° C.
for half an hour, extract with 3 cc< of hot concentrated HNO, or HCl,
dilute, heat, and filter off the SiOf The filtrate is then examined for the

6. If HNO, has been used as a solvent, boil the liquid down to about
I cc, dilute with 20 cc. of water, and if the solution douds on dilution, clear
with a few drops of HNO, and analyze the solution for all groups.

7. When aqiia r^ia is employed, the smallest possible amount should be
used ; the solution should then be evaporated down to about i cc. to destroy
the excess, diluted with 1 5 cc. of water, and the chlorides of Group I. filtered
off and analyzed. The filtrate is treated with 5 cc. of concentrated HG and
again evaporated down to I cc, diluted somewhat, and analyzed for the metals,
beginning with Group II.

8. With few exceptions, the following substances, while insoluble in water,
are dissolved by boiling HCl or HNO, : all phosphates, arsenates, arsenites,
borates, carbonates, oxalates, and tartrates (the allcali salts are soluble in water) ;
also the oxides, hydroxides, sulphides of the heavy metals, alumina, magnesia,
and a number of metallic iodides and cyanides. Oxides of Al, Fe, and Cr
which have heated intensdy do not dissolve readily in these adds.

9. Because of its oxidizing action, HNO^ dissolves sulphides and most
metals and alloys which are not attacked by HG ; the latter, on the other
hand, dissolves the oxides of Sn and Sb, as well as MnOy all of which are

not dissolved by HNO,.

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192 QVAUTATIVE CHEMICAL ANALYSIS

METALS AND ALLOYS

From as to I gram of the metal or alloy, in the form of shav-
ings, foit, filings, or turnings, is treated with 20 cc. of HNOg sp.
gr. 1.2) and is heated gently (under a hood) until no more red
fumes of NO) are given off ; it is then diluted with an equal
volume of water, heated again for a few minutes, and filtered
if necessary. If complete solution takes place, the absence of
Au, Ft, Sb, and Sn is shown ; * in that case, expel the excess of
HNOg by evaporatioa, dilute with water, and analyze the solu-
tion for all groups except IV. and V. Mg, however, must he
included.

(d) If a metallic re^due is left, it is probably Ft or Au t, or
both.

{b) If a white residue is left which is insoluble on dilution
and heating, it may consist of bydrated SnO, or Sb^O^ or both,
admixed with arsenic in the form of tin arsenate, phosphorus in
the form of tin phosphate, bismuth as BigOg, and traces of Cu
and Pb. Filter.

FUtrats. Evap-
orate to drive off
excess of HNO,.
Add Ha to ppt.
ist group and fil-
ter. Analyze resi-
due for Group I.
Treat filtrate with
HtS and filter.
Analyze filtrate for
Group III. and Mg.
Dissolve residue in
hot dil. HNO. and
unite with solution
of residue 2.

Dry and fuse residue in a porcelain crudble with 4
times its wdght of a mixture of equal parts of NajCOi and
S; cool, extract melt with hot water, and filter.

Residue 2 is CuS, BiiSi,
PbS. Dissolve in hot dil.
HNOi and combine with
the corresponding solution
obtained from the first fil-
trate and proceed as di-
rected in the analysis of the
m^n filtrate in Scheme II.

FUtnU will contain the
As, Sb, and Sn as thio-salts
4 an excess of NajS. Just
acidify with HCl, filter, and
reject filtrate. Residue may
consist of AsiSi, SbiSg, and
SnSg + S ; analyze accord-
ing to Scheme II. B.

• Hinnte UDOiintt of Sb dinolve completelf in HNO*; •Qrct aUori containing ■
very unall amannt of Ft are completely diaaolTcd by HNO*.
t A black rendue of carbon or graphite i* x

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INSOLUBLE SUBSTANCES

1. If solution of the alloj does Dot readily take place, and Ft and Au are
absent, treat with HCI ; ttie latter is more satisfactory than HNOa as a solvent
for Al, since the latter is only difficultly soluble in HNOa. HNOi is used in-
Mead of HCI, first, because it is the better solvent for metals and alloys ; second,
because treatment with HQ would convert any P, S, and As usually present as
phosphide, sulphide, and arsenide, respectively, into PHo, HsS and AsHs, which
would be lost by volatilization. HNOg oxidizes these elements to their corre-
sponding acids, vb. : HsPOi, H3SO4 and HaAsOi. Only these acids t<^ther
with HiSiOs need to be tested for in the analysis of alloys.

2. A small white residue may be boiled with concentrated HCI and the
resulting liquid divided into two portions. One portion is tested with Pt and
Zn couple fbr Sb. The other is heated with an iron nail for some time and
the clear decanted solution tested for Sn by the addition of HgCU.

3. A portion of the HNOa filtrate may be tested for HaPO, and HiSO,,
and, if found, P and S reported.

INSOLUBLE SUBSTANCES
By an insoluble substance we mean one which cannot be got
into solution by the action of the acids taken singly or together.
The most common insoluble substances are the following : —
C, S, AgaFeCCN)^. Ag^Fe{CNV AgCN, AgCl, AgBr, Agl,
BaSO,, SrSOj, CaSOi, PbSO^, PbClj, fused PbCrO^, ignited or
anhydrous chromic salts, ignited and native oxides, as Al^Og
(corundum), FcjOj, SnOj (cassiterite), CrjOg, CrjOg ■ FeO
(chrome-iron ore), CaFj, SbjO,, Fe4[Fe(CN)g]a, SiOj, and cer-
tain silicates.

Carbon is generally recognized by its black color, insolubility
in agt^a regia, and combustibility when heated strongly on plati-
num foil. When heated with KNO3, deflagration ensues with
the formation of K2CO3 ; this method is not applicable to graph-
ite, the presence of which may be determined by its physical
properties.

Solphtir is recognized (in the preliminary testing) by the for-
mation of a yellow sublimate and evolution of SOg when heated
in a glass tube.

When S and C are present, it is desirable to remove them by
roasting in an open porcelain crucible.

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194 QVAUTATIVE CHEMICAL ANALYSIS

Treatment with agua regia will have converted the simple
and complex cyanides, as well as all the halides of Ag, into
AgCl; the latter dissolves to a large extent in the strong acids,
but separates out again when the latter are diluted. Long
treatment with aqua regia will dissolve pnissian blue, but the
following method is preferable for complex insoluble cyanides
in general : Boil the substance with a strong solution of NaOH,
dilute and filter ; the residue will contain the heavy metal as
hydroxide, while the filtrate will contain the acid radical in the
form of the Na salt and may be examined by the methods
already given,*

PbSO^ and PbCl, may be dissolved by treatment with hot,
strong NH^CjHgO] solution. The extract is divided into three
portions: in the first, test for Fb by the addition of a little
H,S04 or KjCrO^ ; in the second, test for CI by diluting, acidi-
fying with HNOg, and adding AgNO^; and in the third, test
for SO4 by acidifying with HCl, filtering if necessary, and add-
ing BaClj

Sulphates of the AUcallae Earth Metals are best fused in a
platinum crucible with five times their weight of anhydrous
NajCOg ; the melt is then completely extracted with hot water,
filtered, and the residue is thoroughly washed with water. The
residue will consist of the carbonates of alkaline earths, which
may readily be got into solution with hydrochloric acid, and
the resulting solution tested in the usual way. The water ex-
tract will contain the acid radical as Na^O^ and an excess of
NaaCOa.

SrSOj, CaSOf, and PbSO^ may be quantitatively converted
into the corresponding carbonates by prolonged boiling with a
concentrated NaaCOj solution. If the residue after filtering
is thoroughly washed free from alkali, it may then readily be
dissolved by acid.

BaSO^ requires several treatments for its complete transfor-
mation by NagCOg solution. One treatment changes about 80
per cent, of this sulphate into carbonate.

* For method of uuJyHii of imoluble donble c;uudM not prediutated by esces
of NkOH, lee pige 151 under Ftrrtcyanida, reaction 3,

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INSOLUBLE SUBSTANCES 195

Fused PbCrO^, Cr^O,, Chrome Iron Ore and Ignited Chromic
Salts are best fused with Na^Og in a nickel crucible or with a
mixture of NajCOg and NaNOg. By this treatment, soluble
Na3Cr04 is formed, which after treatment with water is sep-
arated by filtering and tested for in the filtrate.

SaO] and Sb]04 are got into solution by fusing in a porcelain
crucible with three times their weight of Na^COs mixed with an
equal quantity of S. The melt is extracted with hot water and
filtered. The filtrate will contain the Sb and Sn in the form of
thio-salts ; it is just acidified and the precipitate treated accord-
ing to Scheme II. B.

AljOfl and Vefi^ are fused in platinum with KHSO4 or KjSsOt,
whereby they are converted into soluble sulphates. Fusion with
NagCOj, followed by acid treatment, also takes these oxides in
solution.

Silver Ealldes may be treated by one of the following two
methods : —

1. Fuse with NajCOa in a porcelain crucible. The product
will consist of metallic silver and the sodium salts of the halides ;
extract with water and filter. Test the residue for Ag and the
filtrate for halogens.

2. Treat with Zn and dilute H3SO4 in a crucible or small dish ;
allow the action to continue for 20 minutes, and then filter. Test
the residue for Ag and the filtrate for halogens.

SiOj and Silicates are recognized by the " skeleton " NaPO,
bead.

Silicates are usually decomposed by fusing with five times
their weight of a mixture of equal parts of anhydrous Na,COg
and KjCOg, to which about 0.1 g. of KNOg is added. This will
be taken up more fully in the systematic treatment

CaFa is decomposed by heating the finely ground material
with concentrated HaS04 in a platinum dish or crucible, and
evaporating until no more SO, fumes are given off. The resi-
due will be CaSO^ ; extract it with water for some time and filter.
Test the filtrate for Ca with {SHi^CiOf

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196 QVAUTATIVE CHEMICAL ANALYSIS

STstematlc Treatment of bisolable Substances
Before proceeding with the systematic treatment of a residue
insoluble in acids, it is desurable to make the following prelimi-
nary tests : —

1. Examine the residue carefully with a lens and determine
whether or not the substance is homogeneous.

2. Determine whether free C and S are present : if present,
remove by roasting.

3. Chromic oxide is green and will be made evident by yield-
ing a green bead with NaPOg which is unaffected by the reduc-
ing flame ; at the same time, indications of SiOg or of a silicate
will also be obtained.

4. If the substance is white, treat it with a little {NH4)3S.
If it blackens, the presence of Ag or Pb salts is indicated ; con-
firm as directed in (5).

5. If black or colored, mix a small amount with NajCOg and
heat on charcoal with a reducing flame ; a lustrous malleable
globule shows the presence of either Pb, Ag, or Sn. Flatten
the globule in a mortar and heat with dilute HNOg. A clear
solution indicates the absence of Sn ; a white residue, the pres-
ence of Sn. Divide the HNOj solution into two portions. To
the first add HCl; a white precipitate soluble in NH^OH shows
the presence of Ag. To the second portion add dilute H^SO^ ;
a white precipitate is PbSOj. If no globule is obtained and the
white substance is not blackened by(NH4)aS, the absence of Pb
and Ag is shown.

6. Flame Test Take up some of the material on a mois-
tened Pt wire and hold in the reducing flame for some time.
The reducing flame will change the sulphates of the alkaline
earths to sulphides. Moisten the wire with a drop of HCI and
hold in the colorless bunsen flame. Alkaline earths impart
their characteristic colorations to the flame.

7. If test 3 above is found unsatisfactory for SiO, and Cr,
the following may be used ; —

SiOg. Mix the finely powdered substance in a platinum cru-
cible or lead tube with a small quantity of CaF, (SiOj free), add

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SCBEUB FOR INSOLUBLE St/BSTANCES 197

concentrated HjSOj, and warm. Hold in the escaping vapors
a drop of water on the loop of a Pt wire ; if the drop becomes
turbid, SiOj is present

Chromiom. Prepare a Na,COg bead. Take up a little of the
substance mixed with KCiOg and heat Place bead in about
1 cc. of water and heat, A yellow solution indicates Cr.

Scheme for the Treatment of Insolable Substances

If the substance contains Pb salts, these may readily be
removed by repeatedly digesting with hot {NHj)^^!^^©, or
NHfCtHgOg solution, fUtering, and testing the filtrate for Pb,
SOf, and CI. The residue, which should be thoroughly washed
and tested until free from Pb salts [shown by wash water no
longer reacting with (NH4),S], is then treated with KCN solution
to dissolve AgCl, AgBr, Agl, and AgCN, filtered, and washed.
The treatment with KCN is given only when Ag salts are shown
to be present by preUminary test with Zn + HaSO,. The KCN
extract is tested for Ag by adding (NH4)jS, filtering off the
AggS, washing, and dissolving in hot dilute HNO3. To the clear
solution, add HCl; a white precipitate is AgCL If S and C are
present, heat in an open porcelain crucible till all C and S are
oxidized. Mix the substance, now free from Pb and Ag salts, in
a platinum crucible with six times Its weight of a mixture of
equal parts of anhydrous powdered KjCOg and Na^COg + 0,1 g.
of KNOy (If reducible metals have not been removed, treat in
a Ni crucible. Porcelain cannot be used, as it gives up SiOg,
Ca, and Al to the melt.) Heat over a blast lamp till the mass is
in a state of quiet fusion. Remove flame. When cool, transfer
crucible to a casserole or evaporating dish, and extract with
boiling water. Break up the mass with pestle during extrac-
tion. Allow finally to settle, and filter.

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198

QVAUTATIVB CHEMICAL ANALYSIS

FUtnto majr contain NatSiO*, Na,Ci04,
NaF, Na,P04, Na,AIO„ Na,SO„ Na^nO^
Na,AsO« (NaSbOO. Na^nO« Na^BO.
and Na^Of, as well as K salts of these
adds. Divide into two equal portions.

istportioH. Addify with HCl and add
a small portion to the HNOt solution of the
residue j if no ppt. forms, unite the two fil-
trates, evap. to dryness, dehydrate SiOj by
headng at 120° C. till all HCI b driven oE
Extractthe residue with a; cc of cone. HCl,
stir thoroughly, add 25 cc. of water, and
boil with stirring; filter.

Esddne:

Heat filtrate to boiling and
treat with HtS. Without fil-
tering, dilute with cold water
to 100 cc. and saturate again
with H,S. Filter. Analyze
residue for II. A and II. B.
Analyze filtrate for all other
groups.

adportum. Treat for adds.

Residue may consist of BaCO^
SrCO„ CaCO„ possibly ALO,
MgO, Fe,0^ SnO,, andunattadced
SiO„ and in some cases nearly
any metal or its oxide ; wash sev-
eral times with hot water. Treat
with hot dil. HNO, and filter.

FUtrate b to
be united with

HQ solution of
aqueous extract
of melt unless a
ppt. forms ; in
that case, keep

the

olutio

The
ppta. produced
by the same
group reagents
may be united
and examined
together.

Sesidne may
consist of SiOi,
SnOt, and
AI,0,. Fuse in
a Ni crucible
with NaOH.
Extract with
water and filter.
Filtrate con-
tains NajSnO,,
NajAlO, +
Na,SiO,. Test
for AI and Sn,
if not alreadj

Detection of Alkalies in Insoluble Silicates

The J. LavTeace Smith Method. One gram of the finely
ground mineral is first pulverized in an agate mortar with its
own weight of C.P, NH^Cl, and the resulting mixture is then
thoroughly mixed with 8 grams of alkali-free CaCOs and
heated in a covered platinum crucible, gently at first and finally
to a dull red heat, for 40 minutes. The crucible should be
placed in a hole made in a piece of thick asbestos board in such
a way that only two-thirds of the crucible can be directly heated
by the burner. The mass does not fuse but sinters. The active
agent is fused CaCIj, which decomposes the silicate with the
formation of chlorides of the alkali metals. After cooling, the
crucible with its contents is transferred to a casserole, boiled
with water, and the CaO is allowed to slake. The last opera-

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ACID ANALYSIS OF MINERALS, ETC. 199

tion may be hastened by crushing any lumps with a pestle.
After standing for one hour, the mixture is filtered, and the
filtrate is freed of lime by rendering it alkaline with ammonium
hydroxide, heating, adding (NH4)2COg to complete precipita-
tion, and finally a little (NH4)aCa04. Filter, evaporate the
filtrate to dryness, and ignite the residue to drive o£E NH^ salts.
The residue is then treated in the usual way for K and Na.

Acid Analysis of Hiaerals and Metallargical Products

With a few exceptions, minerals and slags need only be
tested for sulphides, carbonates, silicates, phosphates, borates,
sulphates, fluorides, and chlorides. Carbonates and snlphides
may be detected by treatment with HCl, and silica or sili-
cates by the NaPOg bead test. In the HNOg solution of the
finely powdered substance, the tests for phosphates, cbloiides,
and sulphates (in the absence of sulphides) may be made. If
the chloride is present in an insoluble form, as AgCl, it should
be treated by one of the methods already mentioned (see page
195). In the absence of sulphides, the test for sulphates may
also be made by fusing the original substance with NaaCOa, ex-
tracting the melt with boiling water, and filtering ; the filtrate,
after acidifying with HCl and boiling to drive out the CO3, is
then treated with BaClj. If sulphides are present, boil the
finely powdered substance, with constant stirring, with a satu-
rated solution of Na^COg, then filter, acidify the' filtrate with
HCl, and add BaClj; or if the original substance dissolves com-
pletely in HCl, the resulting solution may be treated with BaCIj.
For the detection of flaorides in the presence of silicates, see
test 3 under Fluorides, page 173. For the detection of borates
in silicates undecomposed by concentrated HjSO^, see reaction
6 under Borates, page 1 36.

The tests for borates and flaorides, when these occur together
in combination with silicates, may be carried out in one sample
by fusing about one gram with Na^COg, extracting the mass
with boiling water, and filtering. The filtrate will then contain

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2O0 QUAUTATIVE CHEMICAL ANALYSIS

NajSiOj, NaF, NaBOa + the excess of NaaCO,. A portion of
this solution, after slightly acidifying with HCl, may be tested
for boric acid with turmeric paper. The remainder of the aque-
ous extract is then tested for a fluoride, as described in test 3
under Fluorides (see page i/j).

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TABLE OF SOLVBIUTIES

TABLE OF SOLUBILITIES*

Skewing the classes to which the compounds of the commonly
occurring elements belong in respect to their solubility in water,
hydrochloric acid, nitric acid, or agua regia.

Preliminary Remarks

For the sake of brevity, the classes to which the compounds
belong are expressed by letters. These have the following
signification :

W or w, soluble in water.

A or a, insoluble in water, but soluble in hydrochloric acid,
□itric acid, or in aqua regia.

I or i, insoluble in water, hydrochloric acid, or nitric acid. •

Further, substances standing on the border lines are indicated
as follows :

W-A or w-a, difficultly soluble in water, but soluble in
hydrochloric acid or nitric acid.

W— I or w-i, difficultly soluble in water, the solubility not
being greatly increased by the addition of acids.

A-I or a-i, insoluble in water, difficultly soluble in acids.

If the behavior of a compound to hydrochloric and nitric
acids is essentially different, this is stated in the notes.

Capital letters indicate common substances used in the arts
and in medicine, while the small letters are used for those less
commonly occurring.

The salts are generally considered as normal, but basic and
acid salts, as well as double salts, in case they are important in
medicine or in the arts, are referred to in the notes.

The small numbers in the table refer to notes on the following

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QUALITATIVE CHEMICAL ANALYSIS

SOLUBILITY

i
1

;

0<id.

w
w„
w

w
w

«.
w

w
w
w

».

. w
w

I
w

W-A

A-I
A

W-A„
A

Aftl

W&I„

■mtd

A-l
A»

F«iocTuid>

Chloiue

AA*IlU*

■

Notes to Table of Solubilities

1. Potassium dichroroate, W.

2. Potassium borotartrate, W.

3. Hydrogen potassium oxalate, W.

4. Hydrogen potassium carbonate, W.

5. Hydrogen potassium tartrate, W.

6. Ammonium potassium tartrate, W,

7. Sodium potassium tartrate, W.

8. Ammonium sodium phosphate, W.

9. Acid sodium borate, W.

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TABLE OP SOLUBILITIES

]

Ji&i

-A*.

Oiida

A-X

ChroDoR

W-A

A-I

"«

■

W-.

Pbcphu.
Bd»lc

Oisdue

Fluorkk

■

;

Cubonuc

smStP

w-l

A-l

T«

W-Aa

w„.„

w«

W-A„

Cblwkte

Bntoide

W-A

«i.

lodi*

■

Fcnicruida

A«

»n

■a

•a

A««

Sulphidi

-1!_

Niinue
Chlonu

•W

TmntB

Ciuue

Maku

»-»

Succnua

H^i

W-.

■*

Salk^lau

J__

;

Hydrogen sodium carbonate, W.
Tricalcium phosphate, A.
Ammonium magnesium phosphate, A.
Potassium aluminum sulphate, W.
Ammonium aluminum sulphate, W.
Potassium chromium sulphate, W.
i6. Zinc sulphide,'as a sphalerite, soluble in nitric acid with

separation of sulphur ; in hydrochloric acid only upon

heating.
17. Manganese dioxide, easily soluble in hydrochloric acid;

insoluble in nitric add.

IS-

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ao4 QVAUTATIVE CHEMICAL ANALYSIS

i8. Nickel sulphide is rather easily decomposed by nitric

acid ; very difEcultly by hydrochloric add.
19, Cobalt sulphide, like nickel sulphide,
zo. Ammonium ferrous sulphate, W.

21. Ammonium ferric chloride, W.

22. Potassium ferric tartrate, W.

23. Silver sulphide, only soluble in nitric acid.

24. Minium is converted by hydrochloric acid into lead

chloride ; by nitric acid into soluble lead nitrate and
brown lead peroxide which is insoluble in nitric add.

25. Tribesic lead acetate, W.

26. Mercurius solubilis Hahnemanni, A.

27. Basic.merciiric sulphate, A.

28. Mercuric amido-chloride, A.

29. Mercuric sulphide, not soluble in hydrochloric acid, nor

in nitric acid, but soluble in aqua regia upon heating.

30. Ammonium cupric sulphate, W.

31. Copper sulphide is decomposed with difficulty by hydro-

chloric add, but easily by nitric acid.

32. Basic cupric acetate, partially soluble in water, and com-

pletely in adds.

33. Basic bismuth chloride, A.

34. Basic bismuth nitrate, A.

35. Sodium auric chloride, W,

36. Gold sulphide is not dissolved by hydrochloric acid, nor

by nitric acid, but it is dissolved by hot aqua regia.

37. Potassium chlorplatinate, W-I.

38. Ammonium chlorplatinate, W-I,

39. Platinum sulphide is not attacked by hydrochloric acid,

is but slightly attacked by boiling nitric acid (if it has
been precipitated hot), but is dissolved by hot aqua regia.

40. Ammonium stannic chloride, W.

41. Stannous sulphide and stannic sulphide are decomposed

and dissolved by hot hydrochloric acid, and are con-
verted by nitric acid into oxide, which is insoluble in
an excess of nitric acid. Suhhmed stannic sulphide is
dissolved only by hot aqua regia.

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REAGENTS 205

42. Autitnonious oxide, soluble in hydrochloric acid, not in

nitric acid.

43. Basic antimonious chloride, A.

44. Antimony sulphide is completely dissolved by hydro-

chloric acid, especially upon heating ; it is decomposed
by nitric acid, but dissolved only to a slight degree.

45. Calcium antimony sulphide, W-A.

46. Potassium antimony tartrate, W.

47. Hydrogen calcium malate, W.

REAGENTS

With a few exceptions, all reagents should be of the highest
purity obtainable and each sample lot tested before use. The
fact that the bottle bears the label C. P. is no guarantee of its
purity. It is especially important that the reagent be tested for
the presence of the acid or basic radical it is employed to detect ;
£.£"., " arsenic free zinc " should be tested for arsenic by the
Gutzeit or Fleitmann test before being used. Sodium carbonate,
employed in relatively large amounts for fusion purposes, should
be of a high degree of purity, and should be tolerably free from
foreign bases and acids.

Solutions
Acids
- Cone. HCl, sp. gr, 1.2, 39 % HCl by weight
— DiL HCl, 3 H, sp. gr. 1^05, 10 % HCl by weight

— Cone. HNO^, sp. gr. \.^i, 70 % HNOg by weight.

— DU. HNO^y 3 N, sp. gr. i.io, 10 fo HNOg by weight
"' Cone. H^SO^ sp. gr. 1.84, 98 % HaSO^.

DU. H^SOi, 3 K, sp. gr. 1.09, 13 % HaSO^.

Cone. HF, 40 %.
..^Aeetic Aeid, 5 N, sp. gr. 1.04, 30 fo by weight Dilute 285 cc
glacial acetic acid to a liter.

Sulphurous Aeid, H^SO^ a solution saturated at 15° contains
approximately 16.5 % HjSOa.
. tartaric Aeid, 2 H, 1 50 g. in i liter.

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2o6 QVAUTATIVE CBBMICAL ANALYSIS

Aqua Regia, I part of cone. HNOgto 3 parts cone. HCl; to
be prepared only when needed.

H^S gas is prepared by the action of HCl (l :i) on FeS ; the
gas should be washed hy passing it through water before using.

- — ' Cone. Ammonia, sp. gr. 0.90, 28 % NH,.
. . Dil. Ammonia, sp. gr. o.g6, 10 % NHg.

— Sodium hydroxide, NaOH, 4 M.

As the material used for qualitative purposes contains about
10 ^ of water, the amount needed for a 4 If solution will be
4 X 40 X y = 177.7 g. in I liter.

Potassium hydroxide, KOH, 4 H.

The grade used for analytical purposes contains about 20 %
water ; hence the quantity needed for a 4 N solution will be
4 X 56 X f = 280 g. in I liter.
~ Barium hydroxide, Ba(OH)y saturated solution.
^^ Caicium hydroxide, Ca(OH^ saturated solution.

Salts
' Ammonium acetate, NH^CgHgOg. 3 N. 250 g. in a liter.
. Ammonium carionate, {im^COf SO^ free. Dissolve, without
heating, 192 g. of the powdered salt in a mixture of 80 cc. of
NHjOH{sp. gr. cgo^nd Jcw cc. of water. When solution is
complete, dilute to i Uter. The strength is approximately 4 H.
■' Ammonium chloride, NH4CI, 4 K. 214 g. in i liter.

— Ammonium molybdate solution. To a mixture of 271 cc. of
cold distilled water and 144 cc. of NH,OH (sp. gr. 0.90), add
too g. MoOg and stir till solution is complete ; slowly add this
solution with constant stirring to a mixture of 489 cc. HNOg
(sp. gr. 1.42) and I148 cc. of water. Allow the mixtiu'e to
stand for 24 hours and then decant the clear liquid into a bottle.

Ammonium oxalate, ^^K^)^^0^ ■ HjO. 35-54 g- in I liter.

Ammonium sulphide (colorless), (NH4)aS. Saturate 3 parts
of NHjOH with HjS, add 2 parts of ammonium hydroxide,
and dilute with an equal volume of water.

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REAGENTS 207

Ammonium sulphide (yellow), (NHi)^,. Digest the color- -
less undiluted (NH4)jS with flowers of sulphur in the proportion
of I g. to the liter and then dilute with an equal volume of water.
■'^^^^'Ammonium sulphate, (\^^^^0^^ H, 100 g. in i liter.

■""^ Barium chloride, BaClj • 2 H^O, N. 122.17 g. in i liter.

^Bromine water, saturated solution.

-Calcium chloride, CaClj, anhydrous, M. 55.6 g. in i liter.
Calcium sulphate, CaSO^ • 2 H3O, saturated solution.
Chlorine water, saturated solution.

Cobalt nitrate, Co(NOg)2 • 6 HjO, for confirmatory tests for Al
and Zn. 0.5 g. in i liter.

Copper sulphate, CuSOi ■ 5 HaO. 2 H. 249.6 g. in i liter.
Dimethylglyoxime. Dissolve S g. in 500 cc. hot 95 9J1 alcohoL
Ferric alum, Y&4^0^ • (NH4)jS04 ■ 24 H3O, saturated solu-
tion.

Ferric chloride, FeClg ■ 6 HjO,* 2 H. 180 g. in i liter.
Ferrous sulphate, FeSO^ - 7 HjO. To be prepared in small
amounts as needed.

Hydrochlorplatinic acid, HjPtCl, • 6 HjO. 10 % solution.
Hydrogen dioxide, 3 %■
~^=-.Lead acetate, '^^S^^O^ ■ 3 HjO,t N. 189.5 g. in i liter.
Magnesia mixture. Dissolve 1 10 g. of MgClg • 6 H3O and
280 g. of NH4CI in a liter of distilled water ; when solution is
complete, add z6i cc. of ammonium hydroxide (sp. gr. 0.90),
then add enough water to make the volu.iie 2 liters.
-^ Mercuric chloride, HgClj. Saturated solution.
^r Phenolpkthalein, ife solution in 50% ethyl alcohoL
Potassium acetate, KCjHgOa. Saturated solution.
__,,Potassium ckromate, KjCrOj, H. 97.3 g. in 1 hter.
Potassium cyanide, KCN, N. 65.2 g. in l liter.
.^ Potassium dichromate, K,CrjO,, N. 73.8 g. in i liter.
^ Potassium ferrocyanide, Yi.^diiz^\, N. 105.7 g. in i liter.

,^ Potassium iodide, KI, — ■ 83,1 g. in i liter.
2 ,

Potassium nitrite, KNOj. 500 g. in i liter.

Potassium permanganate, KMnO^, N, 79,1 g- in i liter.

* Should coDlain a little ftee HQ. t The solutioD should canlaiD some free acetic add.

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308 QUAUTATIVE CBEMICAL ANALYSIS

^ "Potassium tkioeyanate, KCNS, N. 97.2 g. in i liter.

' Silvernitrate, AgNOg, — ■ 42.5 g. in i liter.
4

Silver sulphate, AgjSO^. Saturated solution.

Sodium acetate, NaCjHgOj, 4 H. 328 g. in i liter.
— Sodium carbonate, Na^COa (dry). Saturated solution.

Sodium cobaliic nitrite, NajCo(NOj)a. Dissolve 100 g. NaNOj
in 300 cc. distilled water, slightly acidify with acetic acid, and
then add 10 g. of Co(NOa)a • 6 HjO. Allow the solution to
stand for 24 hours and filter if necessary. As the solution does
not keep very well, only small amounts should be prepared at a
time.

Sodium nitroprusside,'^SLi'Fc'iiiO(Q.l<l\- 2 HjO. 10 fo solutioru
■ Sodium phosphate, NajHPO^ ■ 12 HjO, N. 119 g. in I liter.

Sodium stannite, prepared as needed by adding to a little SnCI^
solution sufficient NaOH solution to redissolve the precipitate
which first forms.

Sodium thiosulphate, NajSjOs • 5 HjO, N. 124 g. in i liter.

Stannic chloride, SnCl4, — • 32.7 g. in i liter.

.^Stannous chloride,* SnClg ■ 2 HjO, — • 56.5 g. in I liter.

— Stannous chloride (for Bettendorif Test). Dissolve 113 g. of
SnCLj ■ 2 HjO in 75 cc. of cone. HCl, and add a few pieces
of C.P. tin foil and keep in a glass stoppered bottle.

Starch paste. Prepared as needed by mixing about I g, of
powdered starch with a. little cold water to form a thin paste
and then adding it to 200 cc. of boiling water ; boil for a minute,
cool, and use. The solution does not keep, owing to the growth
of molds. It may be kept for some time, however, if a pre-
servative such as CSa is added.

• The solution ihould be strongly »cid with HO; the additioii of ft little GP. tin
foil preventi the oxitUtioD of the reagent.

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Solvents

Alcohol, amyl, (CgHj^OH)^ C.P. Used in small amounts in
the test for acetate.

Alcohol, ethyl, (CjHgOH), g$%, sp. gr. 0.815.
Benzol, C,Hg, useful for dissolving sulphur.
Chloroform, CHClj, used for dissolving iodine.
Carbon disulphide, CS^, used for dissolving iodine.
Ether, ethyl, (C3H()jO, solvent for fats and oils.

Dry Reagents
Aluminum turnings, pure.
Ammonium chloride, NH,C1, C.P.
Ammonium nitrate, NH^NOs, C.P.
Borax, NajB40i ■ 10 HjO, C.P. and powdered.
Calcium carbonate, CaCOg, alkali free.
Calcium fluoride, CaF,, SiOj free.
Copper, strips.

Ferrous sulphate, FeSO^ ■ 7 HgO, C.P.
Fusion mixture (Na^COg + KjCOg, dry and C.P.).
Iron filings.
Iron nails.

Lead dioxide, PbOg, free from Mn.

Litmus paper, blue and red ; to be kept in stoppered bottles.
Manganese dioxide, MnOg, C.P. and powdered.
Microcosraic salt, NaNH^HPO, • 4 HjO.
Parafhne, m.-p. 124°.

Potassium acid sulphate, KHSO4, fused, C.P. in small lumps.
Potassium chlorate, KClOg, C.P. powdered.
Potassium chloride, KCl, C.P.
Potassium cyanide, KCN, pure.
Potassium dichromate, KjCrjOj, C.P. powdered.
Potassium ferricyanide, KgFe(CN)g, C.P.
Potassium nitrate, KNOg, C.P. fine crystals.
Sand, sea.

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HO QUAUTATIVE CUEMICAL ANALYSIS

Silica, SiOa, purified.

Sodium acetate, NaCaHjOj. C.P.

Sodium acid carbonate, NaHCOg, C.P.

Sodium carbonate, Na^COs, anhydrous, C.P. powdered.

Sodium dioxide, Na^O,, C.P.

Sodium sulphite, Na^SOg • 7 H,0, pure anhydrous.

Starch, potato.

Sulphur, Sowers.

Tin foil, C.P.

Turmeric paper ; to be kept in glass-stoppered bottles.

Zinc, granulated, C.P.

Zinc, granulated, arsenic-free.

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APPARATUS

LIST OF APPARATUS

2 nests of beakers, Griffin, 1-4.
I graduated cylioder, 10 cc.
I graduated cylinder, 50 cc
I wash bottle with fittings,

750 cc.
4 funnels, 6.5 cm.

1 funnel, lO cm.

2 pieces cobalt glass.

t doz. test tubes (is cm.)

3 ft. glass rod.

3 ft. glass tubing.
2 specimen bottles, 50 cc.
2 watch glasses, 10 cm.
2 watch glasses, 5 cm.
I watch glass, 12.5 cm.

1 florence flask, f. b. 50 cc.

2 evaporating dishes, 10 cm,
2 evaporating dishes, 6.5 cm.
I porcelain crucible.

I horn spatula.

I rubber stopper, one bole,

No. I.
I funnel cleaner,
I sponge.

I test tube cleaner.

} box gummed labels, § 217.

I doz. sheets filter paper, 18.5

cm., S. & S. 59S.
I pkg. filter paper, 12.5 cm.,

S. & S. S9S-
I doz. fluted filters, 12.5 cm.,

S. & S. 588.
I test tube rack.
I test tube holder,
I filtering stand.
I box matches, safety.
I pair forceps (small).
I pipe stem triangle.

1 retort stand (2 rings).

2 bunsen burners, with hose.
I blowpipe.

1 stick charcoal.

2 pieces wire gauze, lO cm,

square.
I triangular file.
I platinum wire.
I platinum foil.
I towel

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aia QVAUTATIVE CBEMICAL ANALYSIS

PREPARATION OF UNKNOWNS

la the making up of unknowns, stock solutions of the concen-
tration I cc. = ICX> mg. of metal are prepared. The quantity of
salt necessary to dissolve in a liter to yield this strength is given
in column $ of the table below. By means of burettes or pipettes
definite quantities of these standard solutions are measured out
into student " unknown " bottles, homeopathic vials of 50 cc. ca-
pacity. For the analysis the student uses 2$ cc. of his solution,
the other half being reserved in case the analysis is to be re-
peated. The amounts of standard solutions pipetted out should
be such as to yield a suitable concentration when the volume is
diluted to 50 cc, i.^., when the unknown bottle is filled. An
example will make this clear. Pipette out into unknown bottle
I cc. NaCl solution, 2 cc. Ca(NO,)j, and i cc. of NH^NOg, a-nd
then fill the bottle with distilled water. Since the student uses
only 25 cc. of this solution, this quantity will contain 50 mg.
Na, lob mg. Ca, and 50 mg. NH^. Qualitative unknowns may
be prepared of such a strength that the total weight of metal
in 25 cc. never exceeds 1.5 grams, though it should usually be
kept within i gram. The minimum will depend upon the scheme
of analysis employed. It may be exceedingly small if the most
sensitive tests are used, £.£■., the spectroscopic tests for the
alkali and alkaline earth metals, the KCNS test for Fe, and
the Marsh and Gutzeit tests for As and Sb. But if it is desired
that the student report roughly the relative proportions of the
ingredients present, precipitation methods will be largely used,
which, by the size of the precipitates they yield, give indications
of the approximate quantities of the metals present In the
latter case, the minimum quantity of metal present in 50 cc. will
have to be much larger than it is in the first case.

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PREPARATION OF UNKNOWNS

TABLE EMPLOYED IN THE PREPARATION OF STANDARD

STOCK SOLUTIONS*

Qo«mtTOF

Salt to u Dig.

G»OT StOBTAVCB

%^^

PnCDTT.

SniNCTH I cc.

lAgNO, . . . .

170

V. 5.»

'3-5

■i7

HgNO.H,0 . .

380

HN^

71.S

140

Pb(NO,), . . .

33'

62.S

160

Pb(C.H,0,).-3H,0

379

54.6

183

lIHg(NO.)»-i(HiO)

333

'h^

167

HgCl,

371

.7-4

•35*

Bi(NO0.sHtO .

484

'hn™*

233

Cu(NO,)i-6H,0 .

=95

V, s-

...s

46s

Cua,3H,0. . .

170

I30

270

CuSC-sHjO . .

249

400

Cd(NO,)i.4HiO .

308

S78

CdOi-aHgO . .

319

140

.96

3CdSO,.8H,0. .

769

V. a.

43-S

230

AsiOj

198

75 -S

( )■

NajHAsO, . . .

170

V. a.

227

NajHAsO,.uH^

403

i«.7

( )'

As.O(

230

150

153

SbO,

226

-^■^hS-

188

SnClr2H,0 , .

225

■89

SnC34sH,0 . .

3S0

v. s.

SnCU

360

v.s.

318

1 Verjt soluble.

■ Tbis amount Teadily diMolvo In i llier of mier coataiufng sog. of Nad.

*33g. in I IHer HO <i : i) giv«> stieiigtb icc^asmga. As.

* 367 g. in I liter will givs strength icc.=50 mgs. As.

• T&iMn &om an article pabUshed in &it«i/ &i. <M^ JWii VoLX^ No. fik br one of H

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QUAUTATIVB CBEMICAL ANALYSIS

TABLE EMPLOYED IN THE PREPARATION OF STANDARD
STOCK SOLUTIONS — CwMmm/

OvAmnTW

Salt TO u Do-

Gbodf Soarucm

'S^

Sdluuutt of

SAiTiMiooPia.

^£sr-

XrmTociTB

iwCoLoWAna

MCTAI.

III Al,(SO0.i8H,O .

£66

107

8.1

( y

A1CI,<H,0. . .

242

ii.i

( )•

A](NO,),.8Hrf) .

261

v.a.

10.3

970

Ct,{S0,),."8H,0.

716

T. s.

14.6

690

K^r,<SO,). 34HO

S-2

( )'

Cr(NO.)..9H,0 .

*»

V. s.

770

Cca,-6HK). . .

»66.s

v.s.

19.6

510

FeS0,7H,0 . .

J78

Soo

Fe(N0.)..9H,0 .

404

v.s.

715

FeCl,.6H,0. . .

270

v.a.

20.7

482

Ni(N0.),.6H,0 .

291

soo

Niat-6H,0. . .

238

v.s.

400

NiS0,.7H,0 . .

280

106

47S

Co(NO.),.6H,0 .

29.

v.s.

SOO

Coa,.6H,0. . .

238

v.s.

24.S

407

C0SO47HJO . .

28t

475

MoSO,-4H,0 . .

233

123

400

MnCWHfl . .

198

150

360

Mii(N0,),-6H,0 .

287

537

ZnSO,.7HtO . .

288

'3S

32-5

445

Zii(N0,),6H,0 .

398

v.s.

455

ZnCl,

•36

v.s.

48. .

308

1 630K. in I IHei will (lire strenfftfa i cc=5o ng, AL
*t$pg. in I liter will give strength ( cc.=5o mg. AL
'igag.iD I titer will give itrength icc=iomg, of Cn

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PSEPARATION OP UNKNOWNS

TABLE EMPLOYED IN THE PREPARATION OF STANDARD
STOCK SOLUTIONS — GwtA««(rf

Qminmow

SalttobbD»

Omour SmntuCK

wlS^

SoUmUTTOF

^„^-

100 ua or
Mrru.

IVBaOiaHjO. . .

244

179

Ba(CtH,O0t-Hrf).

273

300

Sr(NO,),.4H^ .

284

324 -

Sr(NO.), . . .

313

41-3

343

Srai-6H,0 . . .

266

106

304

CiCii

III

v.s.

278

Ca(N0a),.4H,0 .

336

V. s.

S90

VMgSO.-jHjO . .

346

9-7

( )'

Mg(N0,)r6H^ .

356.5

300

9-4

1060

Mga,-6Hrf) . .

M3S

36s

1 1.9

837

NaCl

40 '

350

NaiHPO^iaHiO .

3S8

9.3

( )•

NaNO, . . . .

371

193

KHSO, . . . .

136

V.S.

28.S

350

KNO

JOI

357

NHjO . . . .

394

(NH4),S04 . . .

133

27.5

36s

NH4NO, ....

300

32.5

445

(NH0,HPO4 . .

133

36s

27.5

36s

Lia

16.7

600

LINO. . . . .

c )■

* 515 K- Id I U>er will gnt strength i cc.=50 mg. Ug.
*77g. in I liter will give Etrength i cc.=iomg. Na.

*5Q0g. ini litaTwiUgiieUKngibic«.=50ing.U.

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, Google

Acetite, buic, of AI, 7s.
Cr.78.
Fe (-ic), 84.
sqiuation, 03.
Acetates, action of beat on, 156.
detection, 183.
TeactioDs, 156.
wlutnlities, 156.
Add analysis, general examination, 165.
defined, 8.

prdiminaiy cxanunatjon, 160,
Adds, detection in nunerals, 199.
dissociation, 11.
division into groups, 1 13.
first group, analytical, 168.
descriptive, 134.
pielinunaiy examination for, i6o.
second group, analytical, 176.
descriptive, 143.
qiecial tests for, 168.
third group, analytical, 181.
descriptive, 156.
Agate mortar, 13B.
Alcohol, amyl, 156, 183.
ethji,is«.
reduction of chnnnatea I9 meaoB of,

Alkalies, diaracteristics of, in.
detection in Scheme V., 119.
detection in ^cates, igS.
salts of, reactions, 113.
sdubilities, iii.
Alkaline earths, characteristics of, lor.
detection in Schone IV., loB.
salts of, reactions, loi.
solutnlities, loi.
ADoya, analy^s of, rga.
Aluminate of sodium, decranpodtlon with
add, 71,
decon^NMition with NHjCl, 71,
AluminiiTTi, detection in sdieme of analy-
sis. 98.
salts, chaiactetisdcs, 70.

Aluminum salts, reactions, 70.

scdubilities, 70.
Ammonia, convex salts of, 43, 46, 85,
87, 91.

in drinking water, 1 16.
Ammonium aiseno-molybdate, 51.

carbonate, leagent, zo6.

chlorplatinate, 115.

-magnesium arsenate, 53.

-magnesium pho^hate, I r>.

phospho-molybdate, 131.

salts, detection, 119.
reactions, 115,
solubilities, 115.

sulphide, colodess, 306.

Amyl alcohol, 156, 183,
Analysis, add, genctal, 165.

add, ti minerals, 199.

for metals of all groups, tat,

of alloys, 193.

of Group in. (metals) in the proKuce
(d phosphates, etc, 185.

of insoluble substances, 193.

qualitative, i.

quantitative, j.
Anions, 6.

Antimonic compounds, reactions, 55.
Antimonious con^Munds, reactions, 53.
Antimony, detection in sdieme of Miif-

by Gutzdt Test, 56.

fay Marsh Test, 56.

fay Reinadi Test, 56.
Apparatus, list of, iii.
Aqua Eegia, action of BS on, 61.

as on oxidizing a^ent, 35, 40.

as a solvent, 15, 40, 190.

preparation of, 15, 40, 306.

removal of excess, 6r, igi.
Arsenates, detection, 51, Ag, 171.

reactions of, 51.

reduction with KI, 51.

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3l8

Aneiuttes, reduction iriUi SOt, 39, 51, 5a.

spedal tests foi, si> 171-
Anenic, sdds of, 46.

eenstiveness of ^edal tests for, 50.
Anenic tests, ^>edal :
BettendorS, 50.
Fleitmann, 49.
Gutzat, 49.
Maiah, 49.
Rdnsch, 50.
tsfor, i

49-
in wall papei, 49.
Araenites, detection, 49, 69, 171.
oxidation of, 50.
teactions, 47.
sdulHlities, 47.
special tests for, 49, 171.
Aisne,4<)>

Barium hydroxide, reagDit, 306.

salts, detection in scheme of analysis.

solubilities, loz.
sulphate, decosqiostion of, 103.
Base defined, 9.
Bases, list erf, ao6.
dissociation, la.
Basic acetate of aluminuin, 71.
diromium, 78.
iron {-ic), 84.
Basic acetate separation, 93.
Bead tests with tioiax, 164.

teats with NaPO,, 138, 174, 195, 1
BettendoifF test for As, 50.
Bismuth salts, bade, 43.

soluMlities, 43.

test in sdieme of analysis, 66.
Blowpape tests on charcoal, 163, 164.
Borates, detection in salts, 173.

detection in slicates, 136.

reactions, 135.

solubilities, 135,
Borax bead tests, 164.
Boric add, d^ection, 173.
Bromides, detection, iTiS.

insduble, 14s, 195.

reactions, 145.

sdulnlities, 145.

Cadmium salts, detection in scheme of
analysis, 66.

reactions, 46.

soluhiliUes, 45.
Caldum salts, detection in Bdune of
analy^, loS.

reactions, 106.

sulphate, analysis of, 103.
Carbon, detection of, 193.

removal of, 193, 197.
Carbonaceous resdue, I4r, r6i, 185.
Carbcmates, detection, 16S.

reactions, 116.

solubilities, 136.
Carbonic add, detection, 136, 168.
Cations, 6.
Chlorates, as ondizing agents, 36, 91.

bdiaviot on ignition, 159.

detection, 1S3.

leactions, 159.

stdubilities, 159.
Chlorides, detection in absence of bto-
midea, 177.

detection in presence of bromides and
iodides, 178.

insduble, treatment (d, 144, 195.

reactions, 144.

solubilities, 143.
Chlorine water, reagent, 307.
Chlorplatinate, ammonium, 115.

potassium, 113.
Chromatea, as oxidizing agents, 36.
dichromates, 75.

170.
reacticms, 143.
reduction of, 76.
solubilities, 141.
Chrome-iron ore, treatment of, 195.
Chromium, insoluble compounds, treat-
ment of, 143.
oiidaticHi to chromates, 74.
reactions, 77.
salts, detection in sdieme d audyns,

97-
solubilities, 76.
Chromyl chloride test for chlorides,

17S.
Classification of metals, ag.
Closed tube tests, i6r.
Cobalt nitrate test iot M, 73.
lutrate test for Zn, 93,

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Cobalt salts, detectkn In sdteme of
uulyBis,96.

olidation to oobaltk oon^ouDds,
87, S8.

resctioiis, 87.
O^Hdal As£t, 47-
CoUddal state, 65.
Common ion dFect, 15.
Conductivity, g.

at infinite dilution, 11.

equivalent, 10.

C(q>per salts, detection in sdume of
analysis, 66.

leactimis, 43.

sdubilities, 43.
Cyaiudes, action of heat on, 148.

as reducing agents, 39.

detection, iSo.

reactions of ample, 149.

stdubilities, 148.

Decantation, 3.

Deoompositionof alkaline earth aulfitetes,
103, ig4.

antimony tetroxide, igs.

cassiteiite, 195.

Chcmnium conqiounds (ingcd.)i ^9S-

flnorq>ai, 195.

isnited oxides, 19s.

Prussian blue, 151, 194.

ulicates, 138, 195.

nlver halides, 195.
Dehydration of ^dc add, 139. (
Diduoraates, conversion
76.

reduction with 'H^, 61, 76.

reduction with alcdiol, 61, 76.
Directions foi laboiatoiy wtxk, 3.

Electrolytes, 4.
Electrolytic dissodation, 4.
Equations, complicated, wiitiiigaf, aa.

defined, 10.

factors of, 3a

methods of writing, ao.

products of, 30.
Eth)4 alcohol, 61, 143, 183.
Examination, general, for adds, 165.

prdiminaiy (gcnenl), 160.

Ferric salts, diaiactenstica. Si.

detection in sdione ci analyns, 96.

Fenicyanides, acticai on heating, 15a.

detection, 179.

reactions, ija.

eohibilities, 151.
Ferrocyanides, detection, 179.

reactions, 151.

floIubiUties, r5r.
Ferrous salts, characteristics, 78.

detection in scheme of analysis, 96.
Ferrous salts, oxidation to fenic, 81.

reactions, 79.
PHtrate defined, 1.
Flame tests, 164, 196.
Fleitmann test for As, 49.
Fluorides, characteristics, 13a.

detection in the absence of Si<^, 173.

detection in the presence of SiC^
173-

reactions, t^3.

solubilities, r3a.
Fluodlicates, detection, 170.

reactions of, 135.

Glass, etching of, 133.

Group reagents, 30.

Group I., adds, analytiral, t68.

descriptive, 113, 134.
Group n., adds, analytical, r76.

descriptive, ri3, r43.
Group m., adds, analytical, iSi.

descriptive, 134, rjC-
Group I., metals, analytical, 38.
descriptive, 33.
Group n.. A, metals, analytical, 66,
descriptive, 40.
Group n., B, metals, analytical, 69.
descriptive, 46.
Groiqi m., metals, analytital, 0.
descriptive, 70.
Group IV., metals, analytical, 108.
descriptive, roi.
GroiQ) V-, metals, analytical, 119.
descriptive, 11 1.
Groups, divinon of adds into, 133.

metals into, 19, 3^ 31.
Gntzdt test for As, 4()>

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330

Hut's method, 17B.
Hntiiig in doaed tube, l6t.
oa ch&rcoftl, 164.
with coac. HuSOfc i6a.
Hy<bogeii dioxide, oiidatioii with, 17.

nascent, u a Tcdudng sgcot, 38.
^fdioeen sidphide as Group H. reagent,
61.
tedudng agent, 61.
detection, iSi.
Hydrolysis, salts oi antimoi^, 54.
tnsmuth, 41.
iron {-ic), 81.

Insoluble substances, treatment of, 193.
sdieme of analysis for, 197.

Iodides, dtaracteristics of, 147.
detection, ij6.
insoluble, treatment of, 196.

removal of, in preparatian of solution,

190.
solubilities, 146.

Iron, seeferrotts ani ferric.

Laboratory work, directioDS for, 3.
Lawof the Conservatiou of Elements, ai.
Weight, 31.
Mass Action, 13.
Lead acet&te, reagent, 107.

peroxide as an oxidiziDg sclent, 17.
salts, detection in small amounts, 36.
scheme d analyss,
38,66.
reactions, 35.

removal of, in the analysis ol insoluble
substances, 197.

Magnesia mixture, reagent, 107.
Uagnesium salts, detection in scheme of
anatyss, 11 9.

removal of, ito.

solubilities, iti.
Manganate of sodium, gi.
Manganese salts, detection of small
90.

and tommtioti, 14.
influence of diluticHl, 14,
Mecfidnal prepatstions, arsenic in, 49.
Mercuric salts, detectkm in sduine ot
analy^, 66.
reactions, 40.
Mercurous salts, detectiiMi in sdieme of
uuilyss, 38.
reactions, 34.
Metals, divi^on of, into groups, 31.
(koup L, reactions of, 33.

sdieme of analyss for, 3S.

Groiq) H., A, reactions of, 40.

scheme of analy^s for, 66.

Group n., B, reactions of, 46.

sdteme of analyus for, 69.

Group m., reactions of, 70.

sdieme of analysis for, 96.
Group IV., reactions of, loi.

sdieme of analy^s for, roS.
Group v., reactions of, iii.
scheme of analysis for, 119.
Metals and alloys, analy^ of, 191.
Metaphoaphate bead test for SiOi, 13S,

174, i«. 196-
Metastannic compounds, reactions lA, 60.
■ 60.

Metathesis, 31.
Minerals, analyss for adds, 199.
powdering ot, 13 B,

Nessler's reagent, ir6.
Nit^el salts, diaracte^tics of, 84.
detection in scheme of analysis, 96.

Nitrates, behavior on ignition, 157.
detection, iSt.
distinction from chlorates, 160.

solubilities, 157.
Nitric add, as an oxidi^ng agent, 15.

action on ferrous salts, a$.

action on HiS, 6r.

action da iodides, 190.

detection of free, 1^9.
Nitrites, behavior on iffaOoa, 155.

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Organic nutter, detedioK, i6i, 1S5.

interference of, 185.

removal of, 1S6.
Orthophcaphoric odd, 119.
Oxalates, behavior 01

detection, 171, iSO.

iiit«rfeience of, 185.

leactioQs, 134.

removal of, 186.

solubilities, 134.
Oxidation defined, 13.
Oxidizing agents :

aqua regia, 15.

halogens, 14.

lead peroxide, 17.

potaflMum chlotate, 36.
potasuum dichromate, 16.
potassium permanganate, 17.
removal of, before piedpitstiiig with

H»5, 61.
sodium dioxide, 37.

Permaoganates as oxididiig agents, 37.
Phosphate, meta-, test for SiOi, 138, 174,
19s. "96-

separation, 188.
Phosphates, characteristicl of, IS9.

detection, 173, 186.

interference o^ 185.

removal of, 1S8.

scheme of analyds in the pfeaeoce of,

188.

solubilities, 130.

Phosphoric addi, 139.

Platinum wire, cleaning of, no.

Potas^mn chlorate, 16.

Potassium, permanganate, 36.

salts, detection in scheme of am^ris,

reactions, 113.

stJubilities, X13.
Powdering minerals, 138.
Predpitates, washing of, 1.

Predpitfttion, defined, a.

completeness of, 39.

with HiS, 63.
Preliminary tests, dosed tube, rti.

wilii cone aS04, 163.

with dil. HO, 163.
Prepamtion of sdution for adds, 165.
of solids, 1S9.

Qualitative analy^ I.
Quantitative analy^, i.

Reactions of metals lA Gimq) L, 33.
Group H,, A, 40.
B, 46.
Group m., 70.
Group IV., loi.
Group v.. III.
Ructions, reveraible, 43, 54, 6<^ 73, 81,
83, 84, 100, 103, isC.

Reagents, detection of arsenic in, 4Q.
dry, list of, sag.
group, 39.
list of, 305.
use and care of, 3.
Reducing agents, Ibt of, 34.
Reduction defined, 13.
with carbon, 39.

hydrogen sulphide, 38.
nascent hydrogen, aS.
potassium cyanide, 39.
stannous chloride, 38.
sulphurous add, ig, 51.
Reinsch test for As, 5%
Sb,s6.
Removal trf bromidea, igo.
iodides, rgo.
organic matter, 186.
oxalates, 186.
pho^ihates, 18S.
alicatea, 137, 186.
Residue defined, 3.

n., A, metals ot the oappet group,

66.
IL, B, metalt of the tin group, 69.

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332 I»i

Scbeme m., metals cl the iioa grcnq},
96.
IV., tbe alkaline earths group, to8.
v., the alkalies, 119.
SqmatioD of lA fiom sB, 63, 64.
Silica, tests for, 138, 174, 186, 196.
Silicates, allcaties in, 198.

decoTi^>ositioii by adds, 138.

by.fuaon with alkali cubonate,

139-
by HF, 140-
detection, 174, 186.
reactions, 137.
removal of, 137, 186.
Klver halides, TcmovaJ of, 197.
salts, characteristics, 33.

detection in scheme of anafy^,

38.
teacdons, 33.
tnatmcDt of, 195.
Smith, J. L., method for alkalies, 19S.
So(Uum alumjnate, decompodtion by

cobaltic nitrite, reagent, 308.
dioxide as an oiidiang agent, 17.
!, 91.

phoqifaate bead test, 138, 174, igs,

196.
gJumlHte test for sulphides, 154.
salts, detection in scheme <A analysis.

Solids, preliminary testing cd, i6t.
Solubilities, table of, loi.
Solubility product, 16.
Solution of insoluble substaitces, 193.
preparation of, for analysis, 189.
preparation of, for add analysis,
r6s.
Solvents, list of, log.
Staimic, meta, compounds, 60.
salts, characteristics, 58.

detection in sdume (rf analysis,

69.
reactions, 58.
sdubilities, 58.
Stannite of sodimn, reagent, 108.

Stanmnis salts, diaiacteristica of, 57.

detection in scheme of analysis, 6g.

reactions, 57.

reduction by means of, 38.

solubilities, 57.
Starch iodide reaction, 14S.

paste, prq>aration of, 308.

Strontium salts, detection in scheme of
analysis, 108.
reactions, 105.

sulphate, decomposition of, 103.
Substances, insoluble, 193.
Sulphates, characteristics of, 134.

decomposition of ■ntaliiw earth, 103,
194.

detection, 169.

TCflctions, 114.

sduMlities, 114.
Sulphides, behavior on ignition, 153.

detection, 154, 181.

insoluble, r54.

reactions, 154.

sodium plumbite test for, 154.

solubilities, 153.
Su^hites, characteristics of, 137.

detection, r69.

reactions, 137.

sidubilities, 137.
Sulphur, removal of, 193.
Sulphuric add, detection of free, r34.

prdiminary testing with, 163.
Synthe^s, ai.

Systematic treBtment of insoluble sub-
stances, 196. t

Table for the prqwiation of unknowns,
313.

of sdubilities, loa.
Tartrates, behavior on ignition, 141.

characteristics of, 140.

detection, 175.

reactions, r4o.

solubilities, r4o.
Thenard's green, 91.
Theory of Electrolytic Dissociation, «•
Tliio-antimonate, $6,

-antimonite, 54.

-arsenate, 48.

-arscnite, 48.

-^auates, detection, 179.

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Ilio-cyKii&tes, nactiona, 153.
solubilities, 153.
-stannate, 57.
-sull^te, detection, 169.

Turmeric pi^>er, a 10.
Unkuovras, prepantioii of, a

Vortmajm's method, 178,

Zinc Baits, characteristics of, gi.

detection of , in sdieme of analysis, 9G .

reftctions, gi.

solubilities, 91.
Zinc'idalinumoou;^ acticm o^ tm SbCk,
55-

Piintsd in U» ttDltcd StUa ol Amuick

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